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Studies on larval trematoda of Burnaby Lake, B.C. Sager, Stanley Murray 1950

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STUDIES  ON  LARVAL  TREMATODA  OF  BURNABY  LAKE,  by  STANLEY  MURRAY  SAGER.  A Thesis Submitted i n P a r t i a l F u l f i l l m e n t  of the Requirements f o r the Degree of  MASTER  OF ARTS  i n the Department  of  ZOOLOGY.  THE  UNIVERSITY • OF •BRITISH October, 1950.  COLUMBIA«  B.C.  THE UNIVERSITY O F BRITISH COLUMBIA VANCOUVER, CANADA ZOOLOGY  October 1 3 t h , 1950  Mr. L.W. Dunlap, Librarian, University of B.C. Dear S i r : This i s to c e r t i f y that Mr. Murrey Sager has submitted an acceptable thesis f o r the Master's degree together with an approved abstract. He has successfully passed an o r a l examination on the thesis. Yours sincerely,  Head, Department of Zoology  Associate Professor, Department of Zoology.  ABSTRACT •  .  .....  Six species of larval trematoda were discovered in ihe ittollusca of Burnaby l^ake, B.C. These included two species each of echinostome cercariae, furcocercous cercariae and xiphidiocercariae. Life cycle studies were carried out with each of these larval, species* A series of infection experiments proved one of the„echinostome cercariae to be the larva of Echinoparyphium f ecurvatum. which Was shown to utilize several species of snails at Burnaby Lake as first and second intermediate hosts. Morphological and experimental evidence indicated the other echinostome cercaria to be the larval stage of Echinostomaii revolution, an adult, trematode parasitic in muskrat of Burnaby Lake. Both natural and experimental first and second intermediate hosts of E. revolutum at Burnaby Lake were established. The two xiphidiocercariae were.found to be very similar morphologically* but were classed as separate species on ihe character of the stylet organ. One xiphidiocercaria bears much resemblance to Cercaria. albui, Brooke 1943, the other appears to be an undescribed species. The first intermediate snail hosts for these xiphidiocercariae have been found at Burnaby Lake and a Gammarus species has been demonstrated as being an experimental second intermediate host. Both the furoocercous cercariae discovered appear to be new species. One of these forms bears some resemblance to Cercaria oregonensis. Macfarlane and Macy 1946, and has been found capable of producing a schistosome dermatitis in humans. A high incidence of larval trematode infection exists in the snails  of Burnaby Lake. Area differenceshave been noted.in snail populations and their trematode fauna. Additions have been made to larval trefca*tode distribution and host records.  ACKNOWLED GBMENTS -  I should like to express my very great indebtedness to Dr. James R. Adams for suggesting this problem and for his ever ready encouragement and assistance throughout the experimental work and in the preparation of the manuscript.  This opportunity is also taken to express deep appreciation- to Dr. W.A. Clemens, Head of the Department of Zoology, whose kindness and consideration has made the work possible.  My thanks are due to the following authorities for the identification gf the Burnaby Lake snails — Dr. J.G. Oughton of - * the Ontario Agricultural College who saw that the snails were placed in the proper hands for identification, and Dr. Henry van der Schalie of the University of Michigan, who provided the actual identifications .  - Appreciation is gratefully acknowledged to Game Warden R.S. King of the Provincial Game Commission for arranging to have muskrat secured from Burnaby Lake and to Mr. P. Bettles for the bountiful supply of muskrat carcasses. A special tribute i s given to fellow students Miss M.H. Thorn, who gallantly served in the schistosome dermatitis experiments, and Miss A. Redlich, who uncomplainingly cared for the many host animals used in the l i f e cycle experiments.  To my pare at s I owe my greatest debt and thanks, for without their forbearance and finanoial assistance, this work could not have been completed.  CONTENTS•  Page. INTRODUCTION  .  1  METHODS AND TECHNIQUES  7  MORPHOLOGY AND IDENTIFICATION OF CERCARIAE AND OTHER .., ..... . . . .  LARVAL FORMS  17  C l a s s i f i c a t i o n of Cercariae  17  Echinostome C e r c a r i a No. 1 . . . . . . . . Echinostome Cercaria No. 2 Furcocercous Cercaraa No» 1  X i p h i d i o c e r c a r i a No. 2 . . . EXPERIMENTS TO DETERMINE LIFE CYCLES '-.  22 29  • • • 37  Furcocercous C e r c a r i a No. 2 . . . . . . . . X i p h i d i o c e r c a r i a No. 1  .  . 43 50 .56 60  Echinostome C e r c a r i a No. 1 . . . . . . . . . . 61 Echinostome C e r c a r i a No. 2 • . . • . . . . . . 69 X i p h i d i o c e r c a r i a No. 1 . . . . . . •  72  X i p h i d i o c e r c a r i a No. 2 • ••  • • . • • 77  Furcocercous Cercaria No. 1  77  Furcocercous Cercaria No. 2 • • • •  79  SCHISTOSOME DERMATITIS EXPERIMENTS  8  1  Page. Introduction Methods  .  81  . . ..-  83  Results and Discussion o f - I n f e c t i o n  85  Furcocercous Cercaria No. 1  85  Furcocercous Cercaria No. 2 . . . . . . 85 ECOLOGICAL RELATIONS OF LARVAL TREMATODES OF BURNABY LAKE. 91 C o l l e c t i o n Areas and t h e i r S n a i l Populations  . . 91  S n a i l Species found at Burnaby lake . . . ... . . .93 Summary of Area Differences i n L a r v a l Trematode I n f e c t i o n « . . . . • • • 96 Degree of I n f e c t i o n of. Burnaby lake Snails . . . 98 Summary of Host Records f o r Burnaby Lake Gercariae  105  Evidence of Host S p e c i f i c i t y of C e r c a r i a . . . 107 Evidence of Multiple I n f e c t i o n of - S n a i l Hosts  9  10*7  Evidence of Ham done t o S n a i l Hosts v . . • • 108 SUMMARY  I H  LITERATURE CITED  116  TABLES •  1. STUDIES ON LARVAL TREMATODA OF BURNABY LAKE, B .C.  INTRODUCTION.  Three aspects of the study of the- l a r v a l trematode fauna of Burnaby Lake, B.C.,  have been of p a r t i c u l a r conoern t o the author;  they are, 1.) to discover what species of l a r v a l trematodes, parfts i t i c as adult worms or Vflukes" i n vertebrates, are harboured by the snails of the area, 2.) to determine the incidence of i n f e c t i o n of these larvae i n the s n a i l s , and, 3.) to trace as f a r as possible t h e i r l i f e cycles i n an e f f o r t to determine what animals of Burnaby Lake figure i n the complicated l i f e h i s t o r y of these worms.  The i n v e s t i g a t i o n of these problems arose i n i t i a l l y a suggestion by Dr. James R. Adams, who ing  the l o c a l intermediate hosts  ( Ondatra zibethica ) .  from  indicated the va&ue i n know-  oi^xhe  Burnaby Lake muskrat  These trematodes must be regarded as pot-  e n t i a l l y epidemic and had already^bhown by Musfeldt ( 1945 ) to be/6i n large numbers i n the Burnaby Lake-muskrat. three trematodes — 1915  (  Her report mentions  Echinostomm coalitum Barker and C.A.  Beaver,  Echinostona-a reviolutum F r o e l i o h , 1802 ). O u i n a u i s e r i a l i s  q u i n q u i s e r i a l i s and Notocotylus urbanensia as being p a r a s i t i c i n t h i s important f u r bearer.  A subsequent  comprehensive survey of  disease and parasitism i n B r i t i s h Columbia muskrat by the same worker ( 1947  ) showed that these same three trematodes are normal  A  parasites of the gut of muskrat indigenous t o several other areas of the province. The l a t t e r report also noted two a d d i t i o n a l trematoda "normal" to B.C. muskrat — Echinoparyphium and Plagiorchis  contigqum  proximus.  In view of t h i s high incidence of trematode i n f e c t i o n i n B.C. muskrat, a survey- of the Mollusca of Burnaby Lake, with respect to t h e i r r o l e as intermediate hosts of trematodes, appeared ed.  warrant-  The vulnerable part of trematode l i f e h i s t o r i e s i s the i n t r a -  molluscan stage and the determination of the s n a i l species concerned with t h i s stage i s r e q u i s i t e t o any type of control measure.  However, a preliminary survey of the Mollusca of Burnaby Lake showed that they contained several species of trematodes i n hosts other than muskrat.  found  The problem then appeared wider i n  scope than the o r i g i n a l l y proposed survey of s n a i l hosts f o r muskrat to  trematodes alone.  A broader i n v e s t i g a t i o n was f e l t  worthwhile  gain l i f e history data on as many l o c a l trematodes asv>possible.  Burnaby Lake i s a game reserve and as such harbours many animals which Can and do act as hosts t o several adult  trematodes.  The report, then, was redesigned t o include the three p a r t i c u l a r aspects mentioned e a r l i e r , i n the attempt of a comprehensive study of the l a r v a l trematode fauna of a selected area i n the Province.  Little previous work has been done locally on larval  -  trematodes and their hosts. MUsfeldt ( 1945 ) conducted a preliminary investigation into the host cycle of Echinostom«aa revolutum at Burnaby Lake, incidental to her survey of parasitism in the muskrat of the area. -,She found that Physa occidental is was infected with a "stylet" or xiphidiocercariae as well as a " possible nonstylet cercaria". No echinostome cercariae were found. She also discovered what she regarded as metacercariae of an echinostome* which were fed to albino rats in an effort to obtain adult worms. No adult worms were produced. Eggs from Echinostomma revolutum* and the subsequent miracidial stage were also described in detail by Musfeldt. Although she did not find echinostome cercariae to emerge from the 65 P. oceidentalis under examination, she did find rediae containing cysts and active cercariae, " reea'embling those of echinostoirn^". The  H  non-stylet" cercaria was not classed as an echinor-  stome because i t lacked the collar spines and-digesiive system characteristic of the Family Echinostomidae *. MusfeIt concluded that "the alternate hosts of Echinostomwi has^as yet eluded discovery".  Going further afield, i t may be noted that there has been little work done on the larval trematodes of fresh water Mollusca of the Pacific Northwest. What appears to be the earliest work recorded in this area of the continent is that of Miller ( 1925) on San Juan Island, Puget Sound, where he made an investigation of the larval trematode infestation of the fresh water Mollusca.  In add-  ition to the fact that San Juan Island offered particularly favourable conditions for the study of trematode life histories, Miller's work was prompted by the  desireability o£ a study of the larval  trematodes in a section of this continent from which no records have been made." As a result of the survey he found seven new species of cercariae and a high.incidence of infection by-these larvae in the snails of the island. Miller ( 1927 ) latest made a more specialized survey, that of the forked-tailed or furcocercous cercariae in fresh water snails of the same area. This investigation added several more new species to the class and additions to cercarial distribution records.  Some recent work on larval trematodes in the Pacific Northwest has been made in connection with schistosome dermatitis or "swimmer's itch." Macfarlane- and Macy ( 1946 ) investigating a c  case of swimmer's itch in Multnomah County, Oregon, discovered a new species of furcocercous cercaria which is capable of producing dermatitis in humans. As far as can be determined, Hunter et a l ( 1949 ) have done the most recently recorded work in this area. They described a new species of dermatitis-producing furcocercous cercaria^ from Green Lake, within the city limits of. Seattle, Washington. In their report, they state, " is the first record based on experiments/ to show the presence of schistosome dermatitis on the mainland in Washington, and within the city limits of  Seattle." It may be added here that, as far as can be determined, the present investigation describes the first experiments made in thisynrovince to prove the presence of a dermatitis-producing cercaria.  Generally speaking, i t appears that work done in larval trematodes in Canada has been l i t t l e and scattered. McLeod ( 1934 ) and Swales.( 1936 ) have both investigated cercarial dermatitis in Manitoba. A few other Canadian workers have described cercariae in papers connected with adult stages.  No special reports on cer-  cariae have been made from British Columbia.  Actually, the study of larval trematodes appears to have had a relatively short history, with much the greatest progress being made in the last few years. Siebold in Europe did a great part of the early work on,trematodes during the early part of the eighteenth century.  As late as 1909 Luhe is reported to have observed  that up to that date, no cercariae had been identified as belonging to the adult echinostomes. Lebour and Nicoll conducted the first studies on larval trematodes to be made in England, in the early nineteen hundreds. However, i t was not until Brown's work ( 1926 ) that the first life history studies of these worms were undertaken in that country.  Cort ( 1914 ) made the first comprehensive survpy of  cercariae in North America.  In the introduction to this work,  Cort states that " practically nothing is known of the life histories of trematodes of North America.. Even in Europe, where many new adults are being described each year, only a few developmental stages are completely known. One reason for this is to be found in the difficulties involved."  Many of the difficulties of which  Gort speaks s t i l l remain for the worker in this field, but the ever increasing knowledge of these forme^is lessening the apparent, and indeed the actual, complexity of the study of trematode life, cycles; i t i s in no way lessening the interest and fascination which this complexity holds for the investigator.  Although this present investigation is 1 argely an extension of Musfeldt's (1945 ) work on the life cycle of E. revolutum. illuminating more of the life cycle of this species, i t has\,developed into a broader study of the larval trematoda of the Burnaby Lake area.  METHODS AND TECHNIQUES.  The investigation was divided into three parts.;- first the collection of snails at Burnaby lake, secondly, the dissection and examination of snails in the laboratory to detect cercariae and other intramollusoan stages, and, thirdly, the carrying out of infective feeding and exposure experiments to determine, life cycles.  Details of methods and techniques employed in each of these divisions are given here while brief introductions and discussions are added to each section in the text where they are most pertinent. This is done to avoid too much cross referencing since the presentation of the data falls naturally into three somewhat distinct sections. A certain amount of repetition has, been necessary, but only where i t will be of some aid to the reader.  Collection og Snails: Snails were oollected from three areas of Burnaby Lake. These areas have been designated as 1.) Laut Park Area, ,2.) S t i l l Creek Area and 3.) Deer Creek Area.  ( See Plate X ) .  A description of each area is given in the section titled M  Ecology of the Molluscan Hosts  Snails were collected over a period of one year, from March 1949 to April 1950, with principal collections confined to . the summer and f a l l of 1949.  A l l collections were made personally.  8. No attempt was made to separate the Mollusca as to species at the time of collection. A l l snails found in an area were placed in common pint-sized jars in which they were carried to the laboratory.  Segregation and Maintenance of Snails•  In the laboratory the snails were washed and cleaned-in i, tap water, segregated as to species and then placed in pint-sized glass jars which served as aquaria throughout the period of observation. Only those snails from the same collection and of the same species were placed together, with no more than twelve specimens, or six large ones, in each aquarium. These aquaria were labelled with a code number which gave the date and area of collection.  - Lettuce, in both fresh and dehydrated states was the principal food supplied the snails. Most species thrived well on this diet which was chosen because of its availability and freedom from infection by larval trematodes. Water in the jars was changed once a week or oftener i f i t became clouded or so stained by the solution of the dried lettuce that observationfor cercariae in the water was made difficult. The snails were kept at room temperature, which varied from 15 *C. to 20 °C. Small quantities of calcium sulphate as suggested by Swales ( 1935 ) and calcium carbonate ( Stiles and Goldberger 1910 ) were occasionally_added to the aquaria to supply the calcium required by the snails. Only  f r e s h unchlorinated water was used.  Detection of Cercariae:  Once segregated and l a b e l l e d , the s n a i l s i n aquaria were observed every two hours f o r the f i r s t week f o r the emergence of cercariae, and at l e a s t once i n every twelve hours a f t e r t h i s f i r s t week. Observation was best done by looking through the illuminatedwater when the aquarium was held up t o a beam of l i g h t .  Echinostome  and s t y l e t cercariae appeared i n t h i s manner as small white opaque objects about 0.5 mm. i n diameter-moving r a p i d l y i n the water. Furcocercous cercaiiae look l i k e f i n e h a i r or dust p a r t i c l e s i n rapid motion.,  I s o l a t i o n of Infected Snailst  S n a i l s shed l a r v a l trematodes anywhere, from twelve hours to two months after c o l l e c t i o n . the  When cercariae were detected i n  water, a l l snails were removed, washed and dried and then  i s o l a t e d singly into small jars containing f r e s h water.  The s n a i l s  which were subsequently found t o be shedding the cercariae were then given a s p e c i f i c number, appended t o the code number of the parent aquarium colony.  Each s n a i l shedding cercariae was l a b e l l e d  i n t h i s manner and separate records kept f o r each of the times of emergence, behaviour data and so f o r t h .  :  lo.  Detection of Intramolluscan Stagesi  I f no cercariae emerged from a group of s n a i l s within one week after collection; some of the specimens were dissected and examined f o r intramolluscan stages.  The s n a i l was removed from i t s  s h e l l by means of a probe, teased on a microscope s l i d e and examined under low-power. When the body could not be removed i n t h i s manner the s h e l l was removed piecemeal.  A l l whole s h e l l s were preserved i n  small s h e l l v i a l s and l a b e l l e d with a code number.  Snails p a r a s i t i z e d by l a r v a l trematodes could be r e a d i l y detected as soon as the s n a i l was removed from i t s s h e l l . cases the spprocysts or recktae " s p i l l e d out  M  I n §6me--  when the body was  removed. The large digestive gland or " l i v e r " of infected s p e c i mens was noticeably swollen and pigmented with a brown or yellowbrown colour.  In others the larvae appear as small worm-like objects  under the t h i n outer t i s s u e of* the gland.  Drawings and notes were made on a l l intramolluscan  stages  .found.  Most of the s n a i l s , however, were kept a l i v e as long as possible i n the aquaria and the examination of the intramolluscan stages delayed u n t i l natural death of the animal.  I n t h i s way  w&j^data on such matters as natural emergence periods, duration of c e r c a r i a ! emergence and length of development of intramolluscan  11. stages were gathered.  Technique of Cercaria! Study:  No great departure from the standard techniques.used for the study of cercariae were made. Most morphological data and a l l drawings were taken from living unstained specimens.  In obtaining cercariae for microscopic observation, the specimens were f i r s t located by placing the aquarium before a beam of light and removing one or more of the specimens by means of an eyedropper. When using a cover s l i p a small amount of water to contain the cercaria i s advisable as i t lessens the tendency for the cercaria to be swept to the edge of the glass.  This water containing the active larva was then placed on a microscope slide and the cercaria singled out by placing the slide on a black background. Most of the water was then drawn off with absorbent paper, leaving the cercaria i n a small shallow drop which restricted the compass of i t s movements. This allows for greater ease i n locating and following the animal under the objective of the microscope. A Number 1 cover slip placed on this drop was also useful i n slowing movements and making i t possible to use the o i l immersion objective effectively. .When; u3ing^^o_vep slip a small amount of water to contain the cercaria^is^dvisaMe^as i t lessens xhe^tendency for the cercaria to be swept to the^edge-ofv^he glass.  12. A suggestion on technique from Dr. J.R. Adams proved to be admirably suited to the study of larval trematodes. This is the use of prepared 10$ methyl cellulose for slowing the rapid movement of cercariae. Methyl cellulose is a highly viscous colourless medium which has been used to inhibit the activity of ciliates. The actual technique employed is to make a small ring of methyl cellulose on the microscope slide into the centre o£ which water containing cercariae is placed. The two media, are then mixed with a probe, forming a thick syrup greatly inhibiting the violent cercarial movements but which causes no distortion or breakage of the animal. An additionally attractive feature of this medium is that the cercariae remain alive in i t for a considerable length of time — at least two hours with most species. As far as can be determined, methyl cellulose has not been used previously in the study of cercariae.  Neutcal red has been found to be the most valuable intravitam dye with a l l species of cercariae* A solution of 5 drops of saturated neutral red in 250 cc. water is ideal for both anaesthetizing and staining. This concentration gives but a faint pink colour yet has the effect of slowing the movement of cercariae within ten minutes, and, in the same period of time, giving good differentiation of body parts. Unless neutral red is used in this weak concentration, separation of t a i l from body andoften complete disintegration results. The stain brings out the digestive system well in both living and dead specimens. Neutral red becomes  13. noticeably concentrated in the genital rudiments.  --  Cercariae were fixed according to a method suggested by  Talbot ( 1936 ). The procedure is to add to the water containing stained or unstained cercariae an equal quantity of boiling 1C$ formalin. The other intramolluscan stages were also successfully fixed by this method.  Drawings were made in composite from live unstained specimens only, using both high power and o i l immersion lenses. The camera lucida was used in drawing quiescent and recently dead cercariae, while free hand sketches were made from the active forms. Much focusing is required as the anatomical features are found at all levels of the organisms. For drawing purposes, the flame cell patterns were best traced in the methyl cellulose medium. However, lack of time andoexperience hindered a complete and thorough appraisal of the excretory structures in these larvae.  Unless otherwise specified, measurements given for cercariae have been made on naturally shed living cercariae in a normally extended and quiescent state. No measurements were made on specimens under, the pressure of a cover slip; a few were recorded for cercariae uniformly fixed by the hot formalin method. though some distortion resulted from fixation i t gave much less variability than did the pressure from a cover slip.  Al-  14. L i f e Cycle Studiest  The l i f e cycle studies were of two main types 1. ) i n f e c t i v e exposure and feeding experiments, and 2. ) examinations of naturally infected hosts. Both were designed t o determine the f i r s t and second intermediate hosts and the d e f i n i t i v e hostsnof the l a r v a l trematodes at Burnaby Lake.- The exposure and feeding experiments included M i r a c i d i a l I n f e c t i o n Experiments, Metacercarial feeding Experiments and C e r c a r i a l I n f e c t i o n Experiments.  M i r a c i d i a l I n f e c t i o n Experimentst  Eggs teased from adult trematodes or washed from the faeces of adult vertebrate hosts were hatched.  Just p r i o r t o the hatching  of the m i r a c i d i a from these eggs, laboratory-raised s n a i l s were exposed t o attack by these larvae.  C e r c a r i a l I n f e c t i o n Experiments•  Ducklings, g o l d f i s h , s n a i l s and a gammarid species were exposed t o attack by a l l species of cercariae.  The g o l d f i s h and  s n a i l s were laboratory-raised uninfected specimens.  The ducklings  were 48 hours old when used f o r i n f e c t i o n and were taken d i r e c t l y from the incubator t o the laboratory without the p o s s i b i l i t y of becoming infected by trematodes.  The gammarids were obtained from  .  .  _  ,  . _  15.  an ornamental pond on the university campus which, as far as coild be determined, was free of trematode infection.  Ducklings were i n -  fected orally by putting the active cercariae inudrinking.vwaier.  All  the other experimental hosts were exposed by being pit ced i n large numbers of active cercariae for varying lengths of time.  Metacercarial Feeding Experimentst  The cystic or metacercarial stage of the larval trematodes, excepting furcocercous forms, taken from both naturally and experiment ally infected intermediate hosts were fed to uninfected animals chosen to act as possible adult hosts for the worms. Pigeons, albino rats, guinea pigs, Pekin ducklings and goldfish were employed i n these experiments.  Cysts-were obtained by teasing the intermediate shai hosts i n a Syracuse dish or en a microscope slide.  An experienced  eye can locate these cysts without the aid of a microscope.  They  are then taken up i n a clean medicine dropper and forced down the throat of the experimental host. Some of the rats and guinea pigs were fed metacercariae i n small quantities of milk. Several hours prior to this feeding, the animal was kept without food or water so that the cysts supplied i n the liquid stood a good chance of being eaten.  16.  The methods and techniques used in the schistosome dermat i t i s experiments are given in a following section.  Life cycle data was also gained from autopsy of muskrats, and the examination of naturally infected snails, tadpoles and fish taken from Burnaby Lake.  Cultivation of Snailst  Snail egg masses collected at Burnaby Lake or from snails, kept in the aquaria were hatched and colonies of uninfected mollusca raised for infeotion experiments. In their natural environment these egg masses are found as long sausage-shaped gelatinous masses attached to the substrata, floating articles, blades of shore grasses and on the underside of l i l y pads. In aquaria, the snails lay egg masses on the glass walls, or as is very often the case, oh the shells of their fellows.  The egg masses were removed to fresh tap water and kept at room temperatures. As the hatching period approached, large quantities of fresh and pulverized lettuce were added to the water. Uninfected colonies of-Physa occldentalis« Phvaa of. traskii. Pseudocolumella, Menetus cooperi and Gyraulus vermicularis were cultivated in this manner. These molluscs were used in infection experiments when three months and over in age •  17. MORPHOLOGY ANDD IDENTIFICATION OF CERCARIAE AND OTHER LARVAL FORMS.  CLASSIFICATION OF CERCARIAE. -• •  .......  ... .....  Most cercariae have been discovered and described separate-  ly from their adult forms and have, consequently, been named separately. As a result, many species of trematodes have been given two names -- one for the adult worm and one for the cercaria. For example, Echingrata revolutum is actually the adult stage of Cercaria echinata Siebold. Used in this sense, the term " cercaria" is not a genetic name but rather a group naae.. This ladfcbCf correlation between larval and adult forms is due largely to the complexity of trematode life cycles and to the difficulty of ascertaining exactly these life histories.  A l l the specimens met with in this investigation were at the outset given a tentative numerical designation baded on a classification suggested by Luhe in 1909:. Lube's scheme ie s t i l l used by most workers in the field. He divided the cercariae into two main groups on the basis of t a i l structure — those which are separate individuals and thosw which are joined together by their tails into a kind of colony.. The latter forms are a l l marine and are called " Rat-king " cercariae. The f ollowingi.is a key given by Baylis ( 1929 ) and based on Lube's classification.  A.  Cercariae separate I.  Tail well developed.  18.  (a) Body retractile within a chamber formed in the basal part--- CYSTtiCERCOUS. (b) Body not retractile into the t a i l 1. Tail not forked.  .  -.  (a) Tail without bristles. (i) Tail when contracted may be as wide as or wider than body_ 4^PAL0CERCCBS (ii) Tail always considerably narrower than body — - LEPTOCERCOUS.  --'  -  (b) Tail with bristles ( marine - forms -- TRICHOCERCOUS. 2. Tail forked at the tip — FURCOCERCOUS •  II.  Tail stumpy or absent. (a) Stumpy — MICROCERCOUS . (b) Tail not developed — "CEKCARIAEUM".  B. Cercariae joined by their tails into a kind of colony — RAT-KING CERCARIAE.  The classification of cercariae is s t i l l very much in a state of flux.  Several schemes have been suggested in recent years  .19. but data on oercariae is s t i l l too meagre to allow for the adoption of any one system. Lebour ( 1911 ) quoted by Dawes ( 1946 ) presented a classification which lays emphasis not on stnucture but upon the mode of .origin. The main divisions in this classification are based on whether the cercariae develop in sporocysts or rediae. Thus-it is a scheme based on life history, since subdivisions are made on type of final host. Faust ( 1924 ) suggested a cercarial classification based on those structural systems which are least modified in the course of development. Of a l l classifications, this one appears to have * had the largest following. However, there has been much doubt expressed by recent workers as to the reliability of using the excretory system as a basis of cercarial classification. This is due mainly to the apparent inconsistencies in the flame cell " formulae" and to the fact that cercariae  M  accurate tracing of the excretory systems of  is exceedingly difficult, even with suitable  apparatus and. abundance of living material" ( Harper, 1929.) Stunkard ( 1929 ) is also of the opinion that the excretory system is not an infallible guide to the diagnosis of trematodes. In some forms, he points out, there are differences occurring within one family and many show excretory systems which have additions to them in passing from the cercaria to the adult worm. Dawes ( 1946 ) suggests that the cercariae be arranged in natural groups on the basis of this change in the number of ;excretory ducts and flame cells. However, Brown ( 1926 ) is of the opinio* that such an increase i n  number may be " an expression of the phylogenetic needs of the organism, and similarity in the number of excretory units in a group or of groups within the system, the result of convergence in evolution and not necessarily an indication of the phylogenetic relationship." Dawes ( 1946 ) concludes that the flame cell formula or pattern does not necessarily denote phylogenetic relationships and may actually give a false impression of relationship. Errors way arise from too implicit a reliance on one set of organs. Porter ( 1928 J mentions further complications arisingjdn the attempt to classify cercariae. "An additional difficulty has accrued, as various workers on adult flukes differ among themselves as to the exact status of certain groups, with the result that groups considered as sub families by one worker, are given family rank-by. other workers. In such circumstances no classification of larval flukes at present can be really satisfactory." MsjnJBg^and' Identifying the Cercariae Found* As mentioned previously, the cercariae met with in this study could not at the outset be attributed with any certainty on solely morphological grounds to known adult trematodes. Until positive identification could be made, they were given the tentative designations " E.C. rv.and " E.C. 2 " for the echinostome forms, " X.C. 1 " and .". X.C. 2 " for the xiphidiocercariae and "F.C. 1 " and " F.C. 2 " for the two furcocercous specimen^. These names  have been followed throughout the text. In the case of  n  E .C. 1 »• positive identification has .  been-possible by means of direct feeding experiments. On the basis of some gross morphological features, the other larval trematodes have been compared with forms described in the literature and given tentative identifications.. These comparisons were made on the basis of body size, presence or absence of spines and fin-folds, number of penetration glands and methods of swimming and attachment* The larval trematodes described a l l f a l l within.the distome grouping, those which, like adult digenetic flukes have two body suckers with the ventral one always distant from the posterior extremity. More specifically, th© cercariae belong to the leptocercous and furcocercous subdivisions of Luhe's classification;. Leptocercous cercariae have tails which are straight, slender and narrower than the body. The echinostomes^belong to this grouping and are characteristically provided with a head collar and a coronet of stout spines. The xiphidiocercariae are also in this group, and have the anterior end provided with a stylet or boring organ. The furcocercous forms have a narrow t a i l which is forked distally. Echinostome Cercariae. Two larval trematodes shed by the Burnaby Lake Mollusca belong to the echinostome group of cercariae. They have been so identified by the fact that they have a head collar armed with  22. spines. Specific identification has been based on the number and arrangement of collar spines, body size and the character of the t a i l , viz. the presenoe or absence of a t a i l f i n . The flame cell pattern, or formula, was studied in some detail in each case but inexperience and lack of time preventjttg^the gathering of f u l l data on the excretory systems. The difference betweenE.C. 1 and E.C. 2 in body size, number of collar spines and character of the t a i l are sufficient to regard them as separate species. In this respect, Beaver ( 1937 ) states that•cercariae of the genus Echinost omata " exhibit few specific characters by which they may be distinguished.' However, 1  the morphological data taken onthese two echinostomes would appear to indicate that:,they are separate species. Echinostome Cercaria Kb. 1.  ( Plate I ).  Morphology Dimensionst ( Average of 30 specimens ). Body Length Body Width Tail Length Tail Width Diameter ventral suc&er  0.420 mm. ©.095  mm.  0.410  mm.  0.038 mm. 0 .049 mm.  This is a relatively short cercaria, with a spadeliike  EXPLANATION OF PLATE I . E.C. 1  Fig. 1 —  General morphology of E.C. 1.  x 200.  Fig. 2 —  Head region showing arrangement of c o l l a r spines.  Fig. 3 —  Freehand sketch of c e r c a r i a swimming, showing p o s i t i o n of t a i l dorsal t o curled body.  Fig. 4 ~  Metacercaria, with c o l l a r spines v i s i b l e .  Fig. 5 —  Metacercaria, with c o l l a r spines v i s i b l e . x 200.  Fig. 6 —  Body i n l a t e r a l view, showing v e n t r a l position of o r a l sucker and extreme protrusion of v e n t r a l sucker,  Fig. 7 —  x 100.  Cercaria contracted i n swimming, with anterior end curled v e n t r a l l y .  x 100.  Fig. 8 —  Redia containing cercariae. x 100.  Fig. 9 —  Redia.  x 100.  F i g . 10 - Extended c e r c a r i a .  23. body and a stout tapering t a i l . When contracted the body varies • from 0.140 mm. to an extended 0.525 mm.  The t a i l also varies much  in size with contraction and extension, from 0.020 mm. to O'^Tu^mm. at the basal section. Generally, the head and t a i l can be regarded as equal in length. The body is most usually rectangular in shape, becoming somewhat leaf-like when contracted and long and slender when extended ( Figs. 1 and 10 respectivelyi) The most prominent features of the body are the two large suckers ( os and vs ) situated anteriorly and mid-ventrally.  The  ventral sucker lies in the posterior one third of the body. It is larger than the oral sucker and is exceedingly protrueile, projecting at times the thickness of the body out from the ventral surface ( Fig. 6 ). In lateral view the oral sucker is seen to open ventrally ( F i g . 6 ) with the oral opening extending in a posterodorsal direction. The digestive system begins with an opening inthe oral suoker and extends to the ventral sucker where i t bifurcates and continues to the posterior extremity of the body. A pharynx is obvious at the level of the lappets. The anterior collar is prominent and bears 43 or 45 spines ( Fig. 2 ). Due to the overlapping of the lateral group of spines, the exact number of collar spines remains in doubt but-most counts gave the total number as 45.  These collar spines have the  following arrangement — a group of 4 spines in two pairs on each  lappet which are bordered by 7 or 8 unpaired lateral spines. The intervening section is filled by a group of 21 dorsal spines. The dorsal set are arranged in two alternating rows and give these spines the appearance of being grouped in staggered pairs, i.e.. an oral spine placed anterior to an aboral spine. The orals appear slightly larger than the aborals. Collar spination shows up to best advantage after the death of the cercariae and in weak neutral red stain, when the spines appear as clear unstained areas, with sharp black borders. Small cuticular spines are visible under high power on the anterior dorsal surface. These body spines extend to at least the midway point between the two suckers• No spines were observed on the ventral surface. The excretory system can be only indefinitely described. It appears to be made up of two lateral ducts running from the posterior extremity to at least the level of the oral sucker. From these ducts many small branches arise. An extension of the system can be seen running into the basal portion of the t a i l ( Fig. 1 )•• Several scattered flame cells were seen but the presence of large cystogenous cells makes the examination for these cells very d i f f i cult, particularly in the region between the two suckers The t a i l can very readily vary from a short stubby structure to one long and slender, tapering to a point distally. . No f i n membrane is apparent on the t a i l . A distinctive feature of the t a i l  25.  is the presence of U notches " or indentations alongutifie edge ( Fig. 4 ). The notches are most prominent in the basal portion and expecially when the t a i l is contracted. They disappear when the cercaria is in neutral red or at times when the t a i l is extended. The Intramolluscan Stages: Redia ( Figs. 8 and 9 ).  ••  The rediae vary greatly in length. Those with birth pores ;  range from 0.29 mm* to 1.05 mm. long, and 0.10 to 0.19 mm. wide. The diameter of the pharynx averages about 0.114 mm.  The birth  pore ( ji'ig. 8 ), is in the posterior quarter and is best seen *hen the.redia is in profile. Kb such pores are evident-Lin the small, immature specimens. Most of these larvae are pigmented with rust coloured pigment granules.  Others are filled with an evenly distrib-  uted light brown pigment.. The anterior end is more transparent than the rest of the body and appears to be marked off from-the remainder by indentations. In this region the muscular pharynx is very conspicuous, both in small and large rediae.  In some, a short  saccular gut is visible,extending only a short distance posteriorly. These rediae appear to be covered, in the anterior half at least, with small cuticular spines ( Fig. 8 ). Many of the larger forms were observed to contain mature cercariae and a few possessed encysted metacercariae.  Metacercaria  26. ( Fig. 5 )•  The cyst of E.C. 1 is small, circular arid transparent. It is bright yellow in colour. The cyst wall is thick,-clear and obvious forming concentric circles. The outside diameter averages 0.167 mmu, showing a variation of from 0.155 mm. to 0.171 mm. The wall is 0.016 mm. thick. Collar spination can be clearly seen especially under a trover slip using high power or o i l immersion lenses. Portions of the excretory system can also be seen, but since the larva folds over on itself within the cyst, a thorough tracingof ~. ducts is exceedingly difficult. Cysts are found singly or in clumps of up to two hundred in number, located most often in the liver of the the infected snail. Behaviour Datat Swimming These cercariae are very active swimmers. They appear in the water to be small, white objects with a nebulous lashing motion of the t a i l surrounding them. Actually, the body is coiled ventrally ( Fig. 3.) and propelled by the vigourous lashing of the t a i l which action can be observed without the aid of the microscope. They appear to favour the deeper water in the aquaria.  On occasions  when the water appears to be free of them some can often be seen swimming very close to the bottom. When not swimming actively,.,as., for example when under the pressure of a cover slip, these cercariae  27. ,  :  resort to creeping along the substratum by means of alternate attachment of anterior and posterior suckers and elongation and,contraction of the body. In.aged or injured specimens when the t a i l becomes detached from the head,,creeping becomes the .sole means of locomotion. This creeping activity also seems to be characteristic of moribund cercariae. Longevity: E.C. 1 is a relatively short lived larva, but has on one occasion been shown to be alive and active thirty hours after emergence from the snail. -In this experiment a large Physa occidental is shedding E.C. 1 was removed from its shell and p^bed injtap water. The cercariae free in the teased liver tissue were found to be active thirty houes later. Cercariae within the rediae also remain active for this length of time although their movements are slowed considerably. Identification: The most accurate spine counts on E.C. 1 give the number as being 45. This, along with relative body proportions and other morphological features gives the cercaria much resemblande to Cercaria echincparyphium reourvatum as described by Harper ( 1929 ). There is no great discrepency in the body lengths of the two larvae, however i t must be noted that the measurements given for C. echinoparyphium recurvatum are from fixed specimens while those for E.C. 1 are from living forms. The comparison then, must be but a general  one, -It was 'found, however, that carefully fixed specimens of E.C. 1 were consistently smaller in size than the living forms so that the difference in body sized mentioned above not as significant as i t would first appear. Harper's description of his cercaria as having a prominent collar around which there is an incomplete circle of 43-45 collar spines agrees with E.C. l..-,Both also have the.oral spines very slightly shorter than the aboral spines. Cuticular spines posterior to the collar and continuing to about the level of the ventral sucker is also found in both forms. The position and relative sise of the suckers, a prpminent muscular pharynx, t a i l size and structure, and structure of oesophagous and gut are also identical in E.C. 1 and C. Echinoparyphium recurvatum.- Incomplete data on the excretory system for E.C. 1 made a comparison on that score impossible, however, the conspicious elements of this system inE.C. 1 agree with Harper's description in that the excretory vesicle is a single lobe and spherical, connected with two lateral collecting tubules and a single tubule from the t a i l ( Fig. 1 ). The resemblance between E.C. 1 and C. Echinoparyphium recurvatum is found also in the structure of the rediae, except in regard to the small, and apparently, younger specimens. Harper describes the latter as having a pair of mobile- lateral ambulatory processes not observed inE.C. 1. The failure to note these for E.C. 1 may have been due to- a lack of detailed study of the smaller  29.  forms. Both rediae have brown pigment, a large pharynx, thick cuticle and lack of movement in mature specimens. The metacercaria of E.C. 1 is larger than those of C. Echinoparyphium recurvatum. which has a diameter of 0.11 mm. and a wall 0.015 mm. thick. Encystment occurs not only in the same species as with 0. Echinoparyphium recurvatum but also within the same host in which the cercariae develops.  Echinostome Cercaria No. 2. ( Plate II • ) Morphology Dimensions* ( average of 30 specimens ). Bo^y Length Body Width Tail LengthTail Width Diameter of ventral sucker  0.385 mm. 0.098mm. 0.420 mm. 0.035 mm. 0.480 mm.  Unstained specimens of these cercariae are yellow, in colour. When normally extended, the body is long and narrow. It id extremely contractile presenting a great variety of shapes and sizes ( Figs. 8, 9, 10 ). Contraction takes place separately i n the portions anterior and posterior to ihe ventral sucker. The body varies in length from a contracted 0.190 mm. to an extended 0.570 mm.  The t a i l is also very contractile, elongating from  EXPLANATION OF ELATE I I .  E «C. 2 Fig. 1 —  General morphology of E .G . 2.  x 200 .  Fig. 2 —  L a t e r a l view of body, showing protrusion of v e n t r a l sucker and ventral f o l d i n g of edges.  Fig. 3 —  Head region, showing arrangement of c o l l a r spines.  Fig. 4  Cercaria i n contraction, with pronounced collar  region.  Fig. 5 —  Structure  of t a i l and f i n f o l d .  Fig. 6 —  Metacercaria, showing curled worm and d i s t i n c t cyst w a l l s .  Fig. 7 —  Camera l u c i d a drawing of two attached c y s t s . Low power.  F i g . 8, 9, 10 — V a r i o u s shapes of active c e r c a r i a . F i g . 11 —  Freehand sketch of Redia containing  F i g . 12 —  Redia with cyst.  cercariae.  30. 0.09 mm. to 0.65  mm.  The anterior collar and spines are fairly prominent ( Fig. 3 j . The number of spines counted was not consistent, the average count being 37. This variation in collar spine number is due to the difficulty in determining exactly the number of overlapping lateral spines. The arrangement of collar spines appear to be as follows — 5 on each lappet or ventral terminationof the collar, 6 alternating lateral or corner spines and 15 in two alternating rows on the dorsal surface. As in the case of £.0. 1, there is at least an apparent difference in the size of these alternating spines, the- orals being slightly shorter than-the aborals, as with E.C. 1. The difference observed here maybe the result of different angles of insertion. Small cuticular spines appear to cover the entire body surface. They are especially obvious in the shoulder region, just posterior to the collar. These cuticular spines are small and i n conspicuous and can usually be seen under high power magnification only, and in lateral view. The body suckers are large and prominent, and of approximately the same size. The ventral sucker is/in the posterior one third of the body. The digestive system begins with an oral opening in the anterior sucker. The prepharynx is difficult to trace and leads to  31.  a fairly prominent pharynx at the level of the lappets ( Figs. 1 and 3 ). The oesophagus is long, bifurcating just in front of the ventral sucker ( Fig. 1 ), with the two intestinal caeca extending to the posterior/of the body. Penetration glands are best seen in stained specimens . They are in two groups, lateral to the oesophagus, and are 10 or possibly 12 in number. Although the glands are large and prominent in stained specimens, the actual number present is somewhat obscured by overlapping cystogenous cells. The contractile excretory vesicle is in-,two parts, one in front of the other ( Fig. 1 ), in the posterior of the body. From this organ two ducts extend anteriorly and a single duct enters the basal portion of the t a i l . The flame cell pattern is difficult to trace in this cercaria/, principally because small vibratile portions of the excretory ducts obscure the flame cells• Flame eells were seen extending from the region of the vesicle, lateral to the ventral sucker and anteriorly as far as the oral sucker. The t a i l is long and slender, usually longer than the body. A fin membrane or fold is present on this structure. Since the f i n membrane arises vertically from the dorsal surface of the t a i l , i t is not always clearly visible( Figs. 1 and 5 ). The intramolluscan Stages*  The Intramollusoan St ageas Redia and Daughter Redia ( Plate II, Figs. 11 and 12 ) • Almost invariably the liver of the snails infected with rediae and-daughter rediae of E.G. 2 are orange or.brown in colour. These rediae are of variable shapes and sizes but are generally elongate• Mother rediae measure on the average 2.3 mm. by 0.42 mm. In some forms a short saccular gut is visible, as well as.a birth pore near the posterior' extremity. Ambulatory processes are especially prominent in smaller forms. The pharynx measures about 0.120 mm. in large specimens. No flame cells were seen. In many instances these rediae contained encysted cercariae and active cercariae • The rediae are capable of slight independent movement. It is probable that this movement, combined with the appetite of the larvae, cause the damage to the liver of the snail host. The digestive gland of many snails were found to be completely replaced by rediae• Metacercaria ( Plate II. Fig. 11 and 12 ). The cyst is comparatively large and perfectly round, with the outer and cyst walls forming concentric circles. Under high power the young trematode can be seen curled up with the ventral anterior surface in contact with the tif» of the posterior end.  33  Groups of up to 40 - 50 can be found in the infected tissue of the snail• Behaviour Data: Swimming: The single t a i l in rapid movement creates the appearance of several flagellae in motion around the cercaria* Under the microscope the body is seen to be strongly contracted when swimming.^ The t a i l is also somewhat contracted and lashes about close to &nd dors ally to the body. This cercaria/would appear to be swimming on its back. Periodically swimming.ceases and the body is etibetchsd or pushed out. At this time a creeping movement may be commenced along the substratum by means of the two body suckers. The body is alternately stretched and contracted in the regions anterior and posterior to the ventral sucker. There appears to be no definite attraction to snail or tadpole hosts. Contact with the host appears to be random, but once contact is made swimming usually ceases attld creeping begins, e j ^ g r g i ^ i they appear to favour the bottom of the aquarium, where they can be readily detected as opaque, pearllike objects. Longevity: The life os these cercariae was found to be ralatively short, being about 18 or 19 hou>s.  34.  >  Escape process from Snail Host ( Pseudosuccinea columella^^. The emergence of mature E.C. 2 from the tentacles of a Mbllusoan host was observed. A description of the phenomenon is thought of value since, as far as can be determined, no such account has been reported in the literature on larval trematodes. Cercariae were seen emerging from a large Pseudosuccinea columella. They appeared in a canal or duct in the parenchjimatous tissue of the anterior or leading edge of the broad tentacle. At one time five cercariae were observed along the length of this canal, wiggling in quick movements and gradually progressing toward the distal opening. The contractions and extensions of body and t a i l characteristic of creeping movements .were also observed. Within half an hour two cercariae had partially emerged from the canal opening body first while a third made violent motions to free itself, proceeding t a i l first.  At the moment the first two escaped, the  snail reacted by a sharp contraction of its tentacle. Most cercariae did not become free of the host tissue in a single unhindered movement but exhibited difficulty in progressing within ihe canal and wiggling clear at ihe opening. The t a i l of ihe cercaria remained attached to ihe host tissue for"some time, with ihe body lashing about freely in the water. Whenever cercariae did escape quickly from ihe canal ihe tentacle of ihe snail contracted sharply.  Forty-four cercariae were seen to emerge from the tentacle in a period of 11/2 hours. Identification t In gross morphology at.least, E.G. 2 closely resembles Cercaria^ echinos&oma revolutum as described by Beaver ( 1937 ')•• Obvious features of collar spination and general body size exhibit particular similarity. The description of C. echinostoma revolutum as seen by Beaver has 37 collar spines in an arrangement identical to that of E.C. 2. A comparison of excretory systems is impossible since complete data w/ts^not obtained for E.C. 2, but the information that was gathered for this system indicates that the general arrangement of the system in both cercariae is similar. Beaver ( 1937 ) i n discussing the difficulty of obtaining complete data on the excretory systems has this to say, " After long and tedious study on the excretory systemsand so called  flame cell formula" or " pattern " of  this and other species,-1 am inclined to aggee with ternberg-Lund ^ ( 1934, p. 81 ) that while i t is an admirable ambition i t is also a practical failure, and I must confess with him and Tubanqui ( 1932 b) that I cannot with absolute certainty determine the number of £lsme cells in the species." The rediae and daughter rediae of E.C. 2 agree in detail with the description given by Beaver ( 1937 ) for C. Echinostoma revolutum. However, Beaver ( 1937 ) does not mention finding cercariae or metacercariae in the rediae of C. revolutum. This is a  point on which several workers have disagreed.  Faust ( 1917 ) for  instance reported that cercariae did not encyst while s t i l l in the rediae.  37. FURCOCERCOUS CERCARIAE. The furcocercous cercariae have long forked tails into which the body cannot be contracted. They usually develop in sporocysts. Luhe separated 9 forms on the basis of presence or absence of eyespots, character of t a i l and furcae, nature of sporocysts and upon hosts. H.M. Miller ( 1926 ) devised a classification of these cercariae which has become widely used. He subdivided these cercariae into " pharyngeal " and " apharyngeal".  Each of these groups  were subdivided into " brevifurcate", those with furcae less than half as long as the t a i l stem, and the " longifurcate", those cercariae with the furcal rami as long as or longer than the t a i l stem. FURCOCERCOUS CERCARIAE NO. 1 ( Plate III ). Morphology Measurements ( average of 30 unfixed specimens ). Body Length - Body Width Tail stem L'e".«gtJi Tail stem Width Furcae length  0.228 mm. 0.030 mm. 0.247 mm. 0.038 mm. 0.228 mm.  This cercaria is short and relatively stout in general appearance. Unstained specimens are deep yellow in colour. The elongated body is about equal in length, but narrower than, the t a i l stem.  EXPLA1IATI0N OF PLilffE I I I . F.C. 1 Fig. 1 —  '  General morphology of F.C. 1. x 400.  F i g . 2 — Diagram of body region of c e r c a r i a , showing some of the flame c e l l s and ducts of the excretory system. Fig. 3 —  Anterior region, showing p r o t r u s i l e s u c t o r i a l apparatus.  F i g . 4 — Diagram of c e r c a r i a attached to the wall of aquarium. F i g . 5, 6, 7 —  Cercaria i n various t y p i c a l p o s i t i o n s . F i g . 6 shows p o s i t i o n of c e r c a r i a when floating.  Fig. 8 —  Body region i n l a t e r a l view.  Fig. 9 —  Sporocyst  containing cercariae.  F i g . 10 - Immature c e r c a r i a teased from sporocyst.  PLATS I I I .  38.  The body is very contractile, becoming at times a rounded ball ( Fig. 5 ) anterior to the iioa-coutractile t a i l stem. The anterior end is provided with an oral suet oral pouch which can be inverted. The oral sucker is terminal anteriorly; the ventral sucker located just posterior to the centre of the body. One or two rows of short stout spines surround the concavity of the ventral.sucker.;Jkh far as could be determined, there are six pairs ©f penetration glands, three ( in 2 groups ) in the anterior region between-ihe two suckers and posterior to the ventral sucker.  They appear to open at the anterior  tip by at least four ducts which pass through the anterior organ. The digestive system begins with a mouth that opens on the anterior ventral surface, surrounded by the oral sucker and connected with a long oesophagus which bifurcates at the level of the ventral sucker and terminating- a short distance posteriorly. Two vacuole-like structures in the body region between the two suckers are prominent and are considered to be unpigmented eyespots. The excretory system has been only partially traced. Seven flame cells can be counted on each side running laterally to the ventral sucker. A prominent bladder or excretory vesicle is present in the posterior end of the body. Two ducts pass from the vesicle into the tail stem and ramify between the caudal bodies. This ramification extends the length of the t a i l stem and for at least a short distance into the furcae. Spines are confined to the anterior cap region... These small spines extend posteriorly from the anterior tip to almost  39. the end of the anterior organ. There is a sharp deaarcating--Hne where.this spined portion ceases. Neither  spines'W flagellets  are found in t a i l stem or furcae. The tail stem is stout, with strongly notched or.indented edges, due to slight and persistent-contraction. .Thia; portion is apparently non-contractile. This structure contains very obvious and distinctive caudal blocks or bodies which are lai&e cell-like objects stained deeply yellow. There are 14 caudal bodies running the length of the t a i l stem. In freshly emerged cercariae the bodies are somewhat^paired but this arrangement is lost in older specimens.  The posterior pairs are smaller than the anterior few  and are continuous with several smaller bodies extending into each furca. During contraction and extension, the caudal bodies move up and down within the t a i l stem. Behaviour Data. Swimming: These cercariae swim by means of a vigourous movement in which the furcae pull and the body pushes. At rest the cercariae appear as small hair-like dust particles about 1/32 of an inch long. They are often inactive for long periods of time and sink slowly in the water, with the furcae uppermost and at a wide angle to each other.  40. Staining Reaction: Neutral red becomes more concentrated in the body than in either the t a i l stem or furcae. When the ceroaria is .placed in weak neutral red,-the body at first contracts into aisphere. The caudal bodies disintegrate after a short time, followed by the disintegration of the tail stem and furcae. The body very often becomes detached from the t a i l stem in neutral red but keeps alive for as long a time as those which remain attached. Effect of Temperature: Experiments were undertaken to illustrated the effect of temperature upon F .C. 1. It was observed that cercariae subjacted to 25°C. for 15 minutes suffered no effects other than a,slowing of body movements. At 39°C, the cercariae ceased swimming; as soon as the temperature was lowered to 35°C, swimmingrrecommenced. Activity was renewed al^o when the temperature was lowered to 35 C. after being at 40°G. for approximately 10 minutes. The ceraariae died in water at temperature 54°C. Effegt of Light: These cercariae are positively phototactic. On several occasions the cercariae were observed concentrated in the top 2 inches of the water after the aquarium had been under a lighted lamp far 10 minutes. When subsequently kept for a few minutes in diffuse light the cercariae became evenly distributed thrcaighotrb the water.  41. The Intramolluscan Stage ( Plate III ). The Sporocyst: The.sporocysts of F.C. 1 are very long and slender, with l i t t l e modification. Cercariae in a l l stages of development are found in the sporocysts, from the rudimentary bulbous beginnings to the mature active cercariae. The sporocyst averages lo~mm. in length, varying greatly from 5 to. 12 mm.  It averages 0.20 mm. in width.  Most have light brown pigment concentrated in the peripheral regions as a dark narrow border. This pigment is found in a lesser degree throughout the larva. Microscopically, and as seen through the thin wall of the digestive gland, the sporocysts resemble small cestodes, being long slender and cream coloured. The liver or digestive gland of snails infected with this larva are usually in a  gorged  condition  but are not as strongly pigmented as in the case of snails infected with the Echinostome and Xiphidiocercariae. The genital pore is relatively large, located about 0.133 mm. from the posterior end. It averages 0.098 mm. in diameter* There appears to be no localization of cercarial development in these sporocysts* Cercariae of equal maturity were observed at both ends as well as in the central portion of the sporocyst. These sporocysts are capable of independent movement. Identification? The identification of F.C. 1 must remain, as previously  stated, largely in doubt. It possesses features in common with several strigeid cercariae a«^aescribed in the literature and yet ;  iS  has others that do not permit i t to be specifically likened to any particular one. The body dimensions place i t in-the group of longifurcate pharyngeal cercariae under Faustj_s classifications. F.C. 1 resembles Cercaria^ dohema. Cort and Brackett (1937 ) in general appearance, having small spines at the anterior extremity only and with a large number of caudal bodies in the t a i l stem. Furthermore, 0. dohema possesses two very large unpigmented eyespots in the anterior of the body which are not present in F.C 1.  Another strigeid with  caudal bodies almost identical with those of F.C. 1 in shape-and number is G. okobojensist Brooks ( 1943 a ) a species taken from the Iowa Lakes region. The "-notched " or indented appearance of the t a i l stem is apparent in both these cercariae. But, the resemblance fails since the body and furcae of C. okobojensis are almost entirely covered with spines, whereas F.C. 1 possess spines at the anterior tip only. The t a i l stem of the former cercaria al60 has fla&ellets projecting from i t , structures which were not observed in F.C. 1.  A similarity to C. ranae  Dort and Brackett ( 1938 ) ceases because of the lack of spination in F.C. 1.  0. pseudoburti, Rankin ( 1939 ) appears to resemble  very closely F.C. 1 in body size but again the lack of spination and character of ihi caudal bodies of F.C. 1 would appear to give i t a  43 status of its own. It seems highly probable that this cercaria, like the forms mentioned above, is the larval stage of one of the holostome group of trematodes, of, the Family Strigeidae ,&\aill>et, 1919 ( Syn. Holostomidae Brandos, 1890 )•• The adult worms are found in the gut of many birds. The cercariae commonly encyst as' tetracotyles or :  diplostoma in the flesh of fish. Several attempts were made to infect some experimental hosts with this cercaria, andv-will be discussed in a following section. Of the cercariae discussed above which bear a resemblance to F.C. 1, C. ranae, Cort and Brackett ( 1938 ) has been reported to be able to produce diplostoma in tadpoles, causing a fatal bloat disease. This feature of forming enx  cysted larval holostomes- in vertebrate hosts is apparently not common to a l l Strigeidaesimilar in appearancesince none of the experiments performed with F.C. 1 were successful. Rankin ( 1939 ) was also unsuccessful in attempts to infect may fly and dragon fly nymphs, gammarids, tadpoles, fishes and mice with C. pseudoburti Rankin. FURCOCERCOUS CERCARIAE So. 2 < Plate I V )-. Morphology! Dimensions ( average of 30 unfixed specimens ). Body Length Body Width  0.385 mm. 0.059 mm.  EXPLANATION OF PLATE IV. F.C. 2 Fig. 1 —  General morphology of c e r c a r i a .  F i g s . 2 and 3 —  x about 400.  Various shapes of anterior s u c t o r i a l apparatus.  Fig. 4 —  Diagram showing p r o t r u s i b i l i t y of anterior end and terminations of gland ducts.  Fig. 5 —  Diagram of t a i l furcae, showing f l a g e l l e t s of the f i n membrane and terminal excretory p a p i l l a e .  Fig. 6 —  P o s i t i o n of c e r c a r i a at surface f i l m of water.  Fig. 7 —  L a t e r a l view of body region showing protrusion of v e n t r a l sucker.  Fig. 8 —  Sporocyst.  Fig. 9 —  D i s t a l portion of caudal furcus of Cercaria milleri.  T a i l Stem Length  -  0.425 mm.  . T a i l Stem Width  0.052 mm.  Furcae Length  0.285 mm.  F.C. 2 i s a long apharyngeal brevifurcate distornate-cercer!^ closely  resembling the members  group.  The body.and t a i l stem are narrow, the f u r c a l rami stout and  tapering to a sharp p o i n t .  of the Cercaria elvae, M i l l e r , 1923  I n a normally extended condition the body  i s s l i g h t l y narrower than the t a i l  stem.  The most prominent features of the anatomy are two dark pigmented eyesp&ts located approximately 0.020 mm. apart and situated one t h i r d of the body distance behind the anterior sucker.  Another c h a r a c t e r i s t i c and, obvions.-feature of F.C. 2 i s the  large " o r a l bulbous" ( Faust, 1926 ),  i n which i s found the ant-  e r i o r s u c t o r i a l apparatus.. This head organ extends about h a l f way between the o r a l and v e n t r a l suckers. The o r a l bulbous replaces the  suctorial disc of other distomes and i s a c t u a l l y a s u c t o r i a l prob-  oscis ( Figs.2£§ and 4 j , ^  i ^ g e tortuous cephalic gland ducts  open as four spine-like projections from the anterior t i p of the cercaria^ ( F i g s . 4 and 7 ) .  The glands themselves are situated  posterior t o the v e n t r a l sucker. The digestive system consists of an inconspicuous tube which appears t o bifurcate and terminate just anterior to the v e n t r a l sucker.  There i s no pharynx.  The ventral sucker is small and extremely protrusile, often projecting out from the subintegumentous tissue ( Fig. 7 ) . The excretory system has been incompletely traced.. At least three main excretory ducts can be seen, two run laterally to the ventral sucker from the region of the anterior organ to the excretory vesicle* The third appears to run down the mid-line ofiibhe body. Excretory ducts eatend through the furcal rami and apparently terminate at the excretory papillae ( Fig. 2 ). In unstained cercariae the vibratile portions of the ducts, and the flame cells themselves, are pink to mauve in colour. The body is enclosed in a relatively thick, obvious body wall. The t a i l stem possesses few distinguishing features such as were present in the-tatl stem of F.C. 1.  No caudal blocks are  present inE.C. 2* The t a i l stem is non-contractile. The furcal rami;, are short, stout and strongly pointed. They are highly contractile. Transparent.. furcal folds are seen under high power. An obvious excretory-papilla^ is found at the tip of each ramus. The furcal fold can best be seen tinder high power or oil immersion only when the furcae are in contraction. In this condition), flagellats, appearing as long dark lines, can be seen projecting from the furcae. These would appear to be creases in the relaxed furcal fold. The flagellets are O.OlO^mm. .long. Under low power magnification the terminal excretory papillae appear as curved spines on hooks. The papillae are flexible terminations.  46. Morphology of the Other Intramolluscan Stages? Plate IV. F i g . 8.  Sporocysts; The sporocysts are long-and stringy i n appearance, and can be r e a d i l y detected w i t h i n the infected portion of t h e s n a i l .  I n de-  t a i l they are s i m i l a r t o the sporocysts of F.C. 1 and c h a r a c t e r i s t i c of-the, schistosome group as a whole.  They are capable of independ-  ent movement.  Behaviour Data;  Swimmingt  This-cercafcia i s a powerful swimmer. t a i l i s forwardly d i r e c t e d .  I n swimming, the  I n a d i f f u s e l i g h t the cercarias tend  to concentrate at the surface. When crawling, these c e r c a r i a proceed i n measuring worm f a s h i o n . On many occasions these cercariae can be found attached to the-walls of the aquarium by means of the ventral sucker.  This i s  a strong attachment, many of the cercariae being unable t o be l o o s ened with a probe without causing damage t o them. However, i t i s not a permanent attachment f o r they can free themselves and recommence swimming or creeping. The v e n t r a l sucker only i s used i n adhering to substrata.. When f l o a t i n g at r e s t i n the water, F.C. 2 hang v e r t i c a l l y with furcae uppermost and spread wide apart — ely 180 from each other.  at approximat-  4*7 . Longevity:  Several experiments t o ascertain the longevity of F.C. 2 were undertaken.  A f t e r a large number of these forms were shed from  a Physa o c c i d e n t a l i s . the s n a i l was removed from the aquarium and the cercariae kept i n the water at s i m i l a r temperature and l i g h t conditions. 60 hours.  At l e a s t h a l f of the ceroariae were a l i v e and active at  A l l the larvae were dead at 72 hours.  E f f e v t of Temperatures  In several instances i t was observed that infected s n a i l s kept at 13 - 14 C , shed but a few F.C. 2. Whenjthese s n a i l s were placed i n aquaria with water at 20 - 21° C ., the cercariae were again :  shed i n great numbers within the period of an hour. E f f e c t of L i g h t : Some experiments were carried out to showjihe e f f e c t of l i g h t on t h i s c e r c a r i a . A^strong light^'wass placed sunder-an^aquarlum i n a darkened room.  At the outset, a l l F.C. 2 were swimming i n the  topmost 1/3 of the water.  After a period of 15 minutes i n t h i s  lighted condition, approximately 90$ of the cercariae were observed swimming i n the bottom 1/3 of the aquarium water.  Identification: Primarily the i d e n t i f i c a t i o n of t h i s c e r c a i i a ^ has been made on the presence of body s i z e , number of penetration glands,  48. spination, and the presence or-absence of eyespots and furcal folds. On thisjtaasis F.C. 2 appears to bear resemblance to Cercariae oreannensis, Macf arlana and Macy ( 1946 ), C. m i l l e r i i Faust ( 1926 ) which i s a member of the C. elvae group ( Miller, 1926 ). Like C. oregonensis. F.C. 1 has been found to be experimentally capable of producing a dermatitis i n man.  Also similar to C. oregonensis  are the body dimensions, the comparison of which i s given here: F .C . 2.  C. oregonensis M. & M. 1946.  Body Length  0.385 mm.  0.315  Body Width  0.059 mm.  0.690 mm.  T a i l Stem-Length  0.425 mm.  0.426 mm.  0.052 mm.  0.047 mm.  0.285 mm.  0.222 mm.  Tail Stem Width Furcae Length  mm.  In addition both possess eyespots. However, there i s no similarity i n the matter of spination.  In C. oregonensis the body,  t a i l stem and furcae are a l l uniformly spined. Spines i n F.C. 2 are present only at the anterior t i p .  F.C. 2 most certainly i s a member  of the C. elvae group as described by Miller, but i t s specific identification  cannot  be made from the present observations.  It must be pointed out that these comparisons are made on superficial grounds. Faust ( 1926 ) mentions that the essential d i f f erentiating features of the apharyngeal fork-tailed cercariae consist in the michrochemical reaction, as well as the number of the excretory cells or penetration glands»  49. An interesting comparison can be-made here with C. milleri.. Faust 1926. C. milleri i s an aph^ryngeal fork-tailed cercaria^ which Faust described as a new species .from Durban, Natal.  I t i s a form  closely resembling-jsercaria^ elvae. Miller, 1923. The fact that such an exotic form should, bear such resemblance to a local species is worthy of note. The body measurements.of these two forms agree closely, as do the character of eyespots and oral bulbous.  XIPHIDIOCERCARIAE: The xiphidiocercariae are characterized by having an-anterior end provided with a stylet or boring or&an. They are not, however, alone in this respect for the Microcercariae, Rhapalocercous and Cystocercous groups also possess stylets.  According to Porter  ( 1928 ) i t was Diesing i n 1855 who f i r s t used the term xiphidiocercariae to describe these forms. In 1919, Liihe further defined the group and noted that these cercariae have characteristically slender t a i l s , penetration glands and no eyes. Xiphidiocercariae develop i n sporocysts and encystment takes place i n second intermediate hosts. LuheJs four main groups of xiphidiocercariae are Cercaria •wiicrotyle, Cercaria vergulae, Cercaria ornatae and Cercaiia armatae. Cort ( 1915 ) further suggested a Polyadena group. Sewell (• 1922 ) reclassified-the xiphidiocercariae, subdividing Luhe's four main groups and placing the Polyadena group as a subdivision of the Armatae cercariae.  The Xiphidiocercariae found at Burnaby Lake f a l l  within  the Polyadena grouping.  X i p h i d i o c e r c a r i a ^ No. 1 ( Plate V ) • Morphologyt  Measurements ( average of 30 unstained normally extended specimens«)  Body Length  0.216 mm.  Body-Width T a i l Length .  0.094 mm.  ~  0.133 mm.  T a i l Width  Diameter o r a l sucker  0.534 mm.  Diameter v e n t r a l sucker  0.35 mm.  This cercariae i s small and extremely c o n t r a c t i l e . When-^ contracted  state the head i s e i t h e r broad and l e a f - l i k e ( F i g . 13 )  or almost a perfect shpere ( F i g . 16 ) while-the t a i l i s stubby and sharply pointed. The body varies from a contracted diameter t o an extended 0.285 mm. i n length.  0.114 mm. i n  Two prominent body  suckers are present. The o r a l or anterior suoker i s s l i g h t l y smaller than the v e n t r a l sucker which i s located j u s t posterior to the mid-line of the body. When the body elongated the anterior sucker i s e s p e c i a l l y obvious, as a r e s u l t of the greatly narrowed gsftds. portion of the body between the two suckers.. The anterior sucker i s usually directed v e n t r a l l y ( F i g s . 6 and 8 ) and surrounds an  EXPLANATION OF PLATE V . X i*C • 1 Fig.  1 —  Sketch of entire c e r c a r i a showing some s t r u c t u r a l datails .  About x 400.  Fig.  2 —  Cyst, showing p o s i t i o n of curled worm.  Fig.  3 —  Diagram of contracted t a i l .  Fig.  4 —  S t y l e t , dorsal view.  Fig.  5 —- S t y l e t , l a t e r a l view, showing the straight ventral  Fig.  6 and 8 —  surface.  Diagram of anterior end of cercaria showing various positions of s t y l e t and shapes of o r a l opening.  Fig.  7 —  P o s i t i o n of c s r e a r i a while swimming.  Fig.  9 —  Diagram showing lobed structure  Fig.  10 - Metacercaria, showing the extreme c u r l i n g  of t a i l .  of l a r v a . Fig.  11, 12 and 1 3 V a r i o u s shapes of c e r c a r i a .  Fig.  14 — Outline sketch of entire sporocyst.  Figo 15 — sketch of portion of sporocyst containing cercariae.  PLiffii V.  51.  oral opening. Depending upon the state of contraction this opening appears as either a posteriorly directed slit  or^a^aTwide  concavity  surrounded by the narrow muscular border of the sucker. The stylet ( Figs. 4 and 5 ) is embedded in-the anterior sucker, dorsal and anterior to the oral opening. -,It is 0.0196 mm. t  in length, with a point of 0.005 mm. long. The structure of the stylet is seen best in unstained specimens under the pressure of a cover slip.  The pressure of a cover slip causes the mass.of the  cercaria to change from a clouded appearnce to extreme clarity making the sharp outline of the stylet stand out in contrast. In appearance the stylet:'.is a sturdy, nail-like structure, with three bulbous areas on the dorsal and two lateral surfaces near the point. The base is the same size as the rest of the stalk and.the has^ rounded corners.  It is noteworthy that the stylet remains intac*  sometimes long after the tot&l disintegration of the cercaria. Two pair of large penetration glands open by one, or possibly two ducts on the anterior tip of the cercaria near the point of the stylet. These ducts extend in corkscrew fashion almost to the glands near the level of the ventral sucker. F|jr6 spines or hairs are found from the anterior tip of the cercaria to a point 1/3 the length of the oral sucker. No spines are present on any other region of the body surface. The excretory system has been incompletely traced.  V  52.  When the c e r c a r i a i s not swimming the t a i l of X.C. assumes a short and stubby shape ( F i g . 3 ) . shape, the  1  In t h i s contracted  notched " o r crenated appearance of the borders of  the t a i l becomes prominent.  In swimming the t a i l i s g r e a t l y extended,  becoming a long slender pointed structure, l o s i n g i t s notches. crenation disappears  also i n stained specimens.  Tail  A characteristic  feature of the t a i l , when i t i s somewhat extended i s the appearance of four or f i v e bumps or " knots M at regular i n t e r v a l s along i t s length, ( See F i g . 9 ) .  These notches appear to be a c h a r a c t e r i s t i c  or at l e a s t a consistent feature of t h i s c e r c a r i a . They are arranged alternately on each side, with several successively smaller ones i n the d i s t a l h a l f .  Morphology of the Intramolluacan  Staseat  p  i  a  t  e  v  .  }  pige.-i4 n d a  15 ) . The  Sporocystt  The sporocyst?X.C ..,1 are of a great v a r i e t y of shapes and sizes.  Generally, the sporocysts are undifferentiated,, slender,  terminally club-shaped s t r u c t u r e s . 0.209 mm.  to 0.760 mm.  They range i n length from  and i n width from 0.078 to 0.133  mm.  Many  contain the developing as w e l l as mature active cercariae, the l a t t e r being found i n small numbers only.  Stained i n weak neutral  red, the active cercariae within the sporocysts concentrate much more of the dye than does the surrounding m a t e r i a l . Brown pigment i s present i n most of the sporocysts and i s  15  ._ :  ^3.  concentrated in a narrow area bordering the wail. It seems probable that the sporocysts without these granules are the more mature forms in which the pigmentation has been lost. Many of the smaller, presumably younger larvae have a pink colouration. A brown pigmentation colouring the whole of the digestive gland of the snail host almost invariably indicates infection by these larvae. None of the sporocysts examined contained metacercariae. In this respect, care must be taken by the observer to assure that a cyst which appears to be within the sporocysts is actually contained and not, as often occurs, free and merely superimposed or underneath  the c^carVcr"' The Metacercaria; The cysts are colourless, oval shaped bodies. There is an apparent variation in the size of the cysts, which as far as can be determined, is due to-the cysts lying at various angles to the horizontal. In an end view the cyst is almost a perfect circle, measuring 0.122 mm. in diameter. 0.133  The oval shaped cysts are 0.124 x  mm. The wall is narrow but clearly defined. Within the cyst  wall the metacercaria is doubled upon itself so that the stylet in some instances is in contact with the posterior end. Ir£;L^i^ffli--Ml^3trlg., and. figraigia. at least, the cysts were found in small quantities in the mantle cavity and digestive gland.  54.  As stated previously no positive evidence of cysts within the sporocyst was observed. However, in one Helisoma trivoluis. in which sporocysts were found to be in an advanced stage of decomposition objects looking much like decomposing cysts were seen within the larval walls.No definite cyst wall or stylet was observed but the dimensions ( 0.133 x 0,130 ) agree favourably with those found for the cyst of X.C. 1. Behaviour Data; Swimmings Swimming is accomplished by the propelling action of the t a i l aided by a sympathetic rhyt*m)ic movement in the curled body. Just prior to swimming the t a i l is stretched greatly. The body in swimming is bent ventrally and is strongly contracted,, the t a i l lashes about dorsally to the body. Although the swimming activity is vigourous, the cercaria gains l i t t l e distance — virtually no more than i f the animal had spent the time in creeping over the substratum. X.C. 1 has been observed to maintain a rapid swimming activity for about two minutes, then to suddenly commence a creeping movement of sucker trac^tion and body elongation. After a minute or so of creeping, the ineffective swimming is resumed. Older and moribund specimens were found to creep almost exclusively. This cercaria creeps in a fashion similar to that as described for the other cercariae.  55  Action of the Stylet: The action of the stylet organ, presumably used i n this penetration of the 2nd intermediate host tissue, has been observed. Embedded as i t i s i n the muscular anterior sucker, the stylet has j/>re&b mano^uverability. While the animal creeps along the substratum the stylet i s i n constant probing movement. A close observation of this movement reveals that i t i s a lever type, with the fulcrum located at or near the bulbous portion, causing the posterior t i p of the stylet to transcribe large arcs.  That.is, the stylet scoops  down towards the oral opening and then up and out towards the substratum. Longevity; Experiments showed X.C. 1 to be short lived. Penetration and Encystment of Cercaria: On two occasions, X.C. l.was observed i n the process of piercing the surface meniscus of water on a glass.surface.  The .  cercaria was only successful however, i n pushing a channel of water before i t .  In ashort period of time, the creeping movement slowed  and the t a i l ceased lashing about. Later, the t a i l became detached from the body and disintegrated.  An exudate then appeared on the  anterior t i p of the body, preparatory, i t i s assumed, to the formation of an encircling cyst wall.  This was an abortive attempt for  the secretion failed to encircle the body but instead mixed with the  56. surrounding water. for  I t would thus appear that s a t i s f a c t o r y conditions  cyst formation were not present.  The resistance afforded by the  miniscus was possibly a s u f f i c i e n t stimulus f o r the process of cyst formation but the character of the surrounding medium prohibited completion. Ident i f i c a t i on; Due t o i n s u f f i c i e n t morphological data gathered from t h i s species, a p o s i t i v e i d e n t i f i c a t i o n has been impossible.  Other cer-  cariae which show s i m i l a r i t i e s t o X.C. 1 are C e r c a r i a conneae* Brooks 1943, C. d o r o t t i , Brooks 1943', and C. a l b u i , Brooks C. leptosoma  1943,  , Brown 1929, with most resemblance towards the  C. a l b u i .  X i p h i d i o c e r c a r i a No. 2 ( Plate VI ) . Morphology;  Very l i t t l e morphological data and no measurements were made on X.C. 2.  This s t y l e t c e r c a r i a was-seen on but one occasion,  emerging from a large Helisoma t r i y o l v i s h o r n i i ( Tyron ) . i t i s s l i g h t l y larger than X.C. 1.  In size  Unstained specimens are t i n t e d  a deep yellow colour.  The o r a l sucker i s large and i s constantly contracting and r e l a x i n g .  This alternate muscular action r e s u l t s i n the oral  opening f l u c t u a t i n g between a large gaping o r i f i c e t o a narrow s l i t . In the l a t t e r case the oral opening i s directed antero-ventrally.  EXPLANATION OF PLATE V I . X.C.  Fig. 1 —  2  Sketch of entire c e r c a r i a showing some structural details.  Fig. 2 —  Extended cercaria, l a t e r a l view.  Fig. 3 —  S t y l e t , dorsal view.  Fig. 4 —  S t y l e t , l a t e r a l view.  Fig. 5 —  Small sporocyst containing  Fig. 6 —  Metacercaria.  F i g . 7 and 8 —  cercariae.  Diagrams of anterior end showing various shapes of o r a l opening.  F i g . 9 -- Sporocyst.  PLATE VI  The stylet i s simple- i n structure and measures QD.163 torn, long.  I t lacks the bulbous thickenings characteristic of X.C.  1.  It i s located i n the musculature of the oral sucker, dorsalaand anterior to the oral opening. The movement,of the stylet i s identi c a l to that as described for X.C. 1, with a fulcrum near the anterior t i p . The t a i l i s long and slender and averages 0.120  mm. i n  length. Yifhen extended and at rest.the t a i l has several '* knots" along i t s length. Notches or orenations. along the edge of the t a i l are present but not obvious as i n the case of X.G. 1. "  ' "  In many  S  specimen^, the t a i l showed a slight bend toward the l e f t on the basal portion ( F i g . 1 ). Morphology of the Intramolluscan Stages? The infected digestive gland of the snail was swollen to a mass larger i n size than the uninfected portions of the body. Blood red patches covered the external surface, of the digestive gland. This phenomenon had not been observed i n any other infected s n a i l . fhe~sporocysts are •hort, broad and have blunt ends. They range i n length from 0.150 mm. 0.098 mm.  to 0.76 mm.,  with an average width of  Most of the sporocysts have an orange pigmentation.  mature and mature cercariae are present i n the sporocysts.  Im-  The  active cercariae creep along the wall. When the end of the sporocyst i s reached the cercaria contracts and, conforming i t s e l f to the curvature of the sporocyst, proceeds to creep along the opposite  wall.  The parenchymous tissue within the mother larva appears to ,  offer no difficulty to the progress of the cercariae. The Metacercaria: No metacercaria were found in the s n a i l .  Behaviour Data; Swimming; The method of swimming i n X.C. 2 i s indistinguishable from X.C. 1. Occurrence: The Hi. trivolvis from which X.C. 2 everged was collected i n the Deer Creek Area, on April 3 r d . The snail-was found on the surface of the moist mud of the lake-shore. It i s vefy likely that this snail.had been out of water for 6 months, for the water ievel of the lake had been, lowered for this period of time prior to collection. The cercariae emerged from the snail within 12 hours after isolation i n the laboratory. Large numbers were shed for a period of two days.  The snail died on the third day and on examination  was found to be highly parasitized. Ide nt i f io atiion: Insufficient morphological data was gathered to give a positive idejntification to this cercaria.  It seems likely however,  59. that X.C. 2 i s the same cercaria^ as.that described by Musfeldt (-1945 ) and found i n Physa occidentalis from Burnaby Lake. The structure of the stylet organ as described for Musfeldt*s cercaria shows much similarity as that found i n S.C. 2.  60.  -  EXPERIMENTS TO DETERMINE LIFE CYCLES.  Introduction;  The experiments reported i n the following section describe the attempts w i t h each c e r c a r i a to trace i t s development toward the adult stage.of the worm.  This work involved two types of i n f e c t i o n  expe riments; 1. ) C e r c a r i a l I n f e c t i o n Experiments, i n which several species of vertebrate and invertebrate experimental hosts were exposed to attach by each species of cercaria. (a) Experiments using Echinostome and X i p h i d i o cercariae to determine which animals serve as second intermediate hosts • (b) Experiments using the Furcocercous cercariae to determine the adult hosts of these forms. 2. ) Metacercarial Infeotion Experiments, inv.which cysts of Echinostome and Xiphidipcercariae were f e d , i n a number of controlled experiments t o vertebrate hosts t o determine i n which the l a r v a l trematode would a t t a i n adult  development.  A summary and discussion of the r e s u l t s with each cercaria^ follows a b r i e f description of the experiments used with each.  61. ECHINOSTOME: C E R C A R I A E N O .  I .  Cercaria! Infection Experiments; Experiments with Mollusca; 1. ) A small uninfected Physa occidentalis was placed in a small amount of water in  a Syracuse  dish along with approximately 20  E . C . I .  After 22 hrs. the cercariae were no longer seen in the water. The snail was then kept in an aquarium for two weeks. The snail was not examined until two days following its death so that the body was found i n an advanced stage of decomposition. No metacercariae were found. 2. ) A large uninfected P. occidentalis was placed in a stender.dish with 10 E . C . 1 for a period of twenty-four- hours. The snail was then examined. No metacercariae were found. 3. ) A large laboratory bred, uninfected P.- traskii was placed in a small aquarium with a Lymnaeaproxima r o i ^ a l l i shedding E . C . 1. After two days of such exposure the Physa  was crushed and ex-  amined under low pov/er of the microscope. These cysts, identical with the 45-spined systs of E . C . 1 were foiund. 4. ) A^small uninfected P. occidentalis and Pseudosuccinea columella were placed in an aquarium with. a. Lymnaea proxima shedding..E .C . 1. The snails were exposed to cercarial attack for 24 hours, after which they were crushed and examined. Each was found to contain 5-10,  45 spined cysts. 5.) A medium sized Pseudosuccinea columella was exposed for 4 days to E.C. 1 emerging from a large P. occidenialis.  Upon examination  the exposed snail was found to contain approximately 150, 45-spined cysts. Experiments with Vertebratest The vertebrates exposed to attach by E.C. 1 included tadpoles, cat f i s h and goldfish.  Kb metacercariae were found i n any of these ex-  posed animals• Metaceroarial Infection Experiments: Pigeon Experiments: Two pigeons were used i n these experiments.. One bird was fed cysts from an experimentally infected P. occidenialis< and the other was fed cysts, on two separate occasions, from naturally i n fected snails. Pigeon Experiment No. 1. An adult pigeon was kept i n captivity for a period of three weeks. During this time several faecal examinations were made to determine the presence or absence of trematodes i n the alimentary canal.  No eggs were detected i n these examinations and the pigeon  was regarded as uninfected.  The bird was then-fed a crushed medium-  sized P. occidentalis containing at least 5 experimentally infected  63y 45-spined metacercaria. Feeding was accomplished by means of a medicine dropper.  The pigeon was kept f o r a period of two weeks  on a diet of grain and poultry s t a r t e r mash. Faecal examinations were then commenced and kept up bi-weekly f o r a period of 6 weeks. The pigeon was s a c r i f i c e d on the 45th day following infecion.and i t s alimentary t r a c t thoroughly examined. No trematodes were found.  Pigeon Experiment No. 2. Part (a) An adult pigeon was kept-for three weeks i n captivi t y , as i n Experiment No. 1., p r i o r t o i n f e c t i v e feeding.  During  t h i s time, repeated f a e c a l examinations f a i l e d to disclose the presence of trematodes i n the digestive tract,.thus the animal was considered t o be uninfected.  The pigeon was then fed 10 - 15, cysts  removed from a naturally infected P. c f t r a s k i .  These cysts were  i d e n t i c a l , as f a r as could be-determined, with the 45-spined metacercatiae of E.C. 1. Faecal examinations were made every 2 - 3  days  f o r two weeks b u t f a i l e d t o reveal the presence of trematode,eggs i n the gut. The diet of the pigeon throughout the experiment was grain and poultry s t a r t e r mash.  After a period o£ a weeks had elaps-  ed during which no trematode ova could be detected i n the faeces, the i n f e c t i o n was assumed to be unsuccessful and the pigeon again regarded as " uninfected."  Part (b) The pigeon from part (a) was fed a "clump" of 150 or more cysts removed from a n a t u r a l l y infected P. o c c i d e n t a l i s . These cysts included an unknown number of 45-spined cysts and  possibly a,, number of 31-spined cysts.  The pigeon was kept for a  period of 21 days on grain and starter mash. The pigeon was sacrificed on the 32nd day and i t s alimentary canal thoroughly examined. Eight small mature echinostomes were found i n the upper small intestine.  These trematodes possessed 45 Collar spines, and  were tentatively identified as Echinoparyphium recurvatum. A description of this fluke i s given i n a following section. Duckling Experiment: A small number of 37 and 45-spined cysts removed from a naturally infected Pseudosuccinea columella were fed v i a medicine dropper to a small 3 day old duckling. The duckling was incubator raised and thus considered to be uninfected.  I t was fed a diet of  starter mash. M-days following the infective feeding, the duckling was inadvertently destroyed by a predator. An examination of the section of the digestive tract which remained revealed no immature trematodes. Guinea Pig Experiment: 180 or more E.C. 1 cysts removed from a naturally infected Physa occidentalis were fed v i a medicine dropper to an adult guinea pig.  The cysts were teased from the digestive gland of the snail,  6 hours prior to the infective feeding and kept i n water. Movement of the metacercaria within the cyst was observed at the time of feeding.  The animal was sacrificed after 43 days  and its digestive tract thoroughly examined. No trematodes were  65. found. Rat Experiments! Rat Experiment No. 1. 20 cysts identical with those of E.G. 1 were removed from a naturally infeeted Pseudosuccinea columella and fed to an adult albino rat with a^/medicine dropper. Faecal examinations prior to feeding of cysts showed the rat to be uninfected by trematodes. I t was kept on a diet of milk and starter mash for 43 days after i n fective feeding. During this period, no trematodes were found i n the faeces. -On the 44th day the rat was sacrificed and i t s digestive tract thoroughly examined. No trematodes were found. Rat Experiment No. 2. 8 6r 9: forty-five spined cysts taken from a Physa sP were fed v i a drinking milk to a medium-sized albino rat. Faecal examinations were made two and three times a week for a period of 5 weeks after infective feeding. No trematodes were found i n the intestine or viscera when the rat was killed and examined. Rat Experiment No. 3. 15 forty-five spined cysts were fed to an adult albino rat i n milk. The rat was kept for 35 days on a diet of grain pellets, during which time repeated faecal examinations failed to reveal trematode ova i n the faeces. The rat was then fed a clump of  66.  150 or more cysts, containing 37 as well as 45-spined metacercaria©. She rat was sacrificed 31 days after this feeding but no trematodes were found i n its intestine. • The Identification of the Adult Echinostome ( Plate VII ) • The echinostome produced in the pigeon from an infective feeding of cysts of E .0. 1 is, as far as can be determined, identical with-Echinoparyphium recurvatum ( Linstow 1873 ) Luhe 1909. The most obvious features in common with the adult^ cercaiia and metacercaria are the number and arrangement of the collar spines. ( Fig. 5 ). The following is a description of the adult 45-spined echinostome obtained from the pigeon which was fed 45-spined metacercaria identical with E.C. 1. The worm is short and stout and possesses an-obvious head collar bearing 45 rostellar spines ( Fig. 5 ). The anterior 1/3 of the body is bent ventrally almost at right angles to the main axis, as seen in Fig. 1. The dorsal surface at this point forms a distinct shoulder. Posterior to the collar there is a short narrow neck region. A distinctive feature of the anterior portion of the worm is the ventral folding of the edges which results in a ventral groove extending from the pharynx approximately to the ventral sucker. Both body suckers are prominent, the ventral being slightly larger than the oral, and located in the anterior on© third of the .worm. The 45 collar spines appear to have a definite arrangement.  EXPLANATION OF- PLATE VII. Echinoparyphium recurvatum. Fig. 1 ~ Ventral view of adult, showing general morphology and relative body proportions. About x 40.. F i g . 2 ~ Freehand sketch of a portion of the excretory duct showing the direction of activity of vibratile patches along i t s length. Fig. 3 —  Outline diagram of egg. x 30.  Fig. 4 — Lateral view of anterior end, showing position of oral sucker and paired arrangement of the collar spines. Fig. 5 — Ventral view of anterior end, showing the arrangement of collar spines. Fig. 6 — Lateral collar spine. About x 1000.  67.  :  There are three pairs of spines on each lappet, each somewhat spindle-shaped.  Two pair are more anterior than the third group,  and a l l are larger than the lateral and dorsal spines. Bordering each lappet group i s a single spine and then begin the paired dorsal series.  The dorsals form two rows, one the oral, the other  the aboral. These spines are spiked or wedge-shaped i n comparison , with the slightly spindle-shaped lappet spines. Their average length is .057 mm.  The collar spines of thisvworm are b r i t t l e , and resist  dislodgement to a fair degree. When the worms were shaken i n saline and straightened out with a fine hair brush, some of the ends of the collar spines were found to be broken o f f . Cuticular spination, partially represented i n Figs. 1 and 2, extends from the anterior collar to the level.of the ventral sucker at least, on-both the dorsal and ventral surfaces. These spines are i n rows about 0.028 mm. apart. In the neck region the row arrangement of the cuticular spines i s somewhat lost, due, perhaps, to contraction of the cuticle.  The body s~pines are 0.023 mm. long. They  can be seen well i n unstained worms under No. 1 coverslips. Of the internal anatomy, the testes are most prominent. They appear as two oblong structures in the mid-line, just posterior to the centre of the worm. Anterior ioothe testes, the uterus coils several times before reaching the level of the ventral sucker.  In  the mat tare, worm, eggs i n the uterus can be readily seen as very yellow, ovate bodies within the folds of the uterus.  The eggs are  operculate. Vitellariae extend laterally from the ventral sucker to  68, almost the posterior t i p of the body. Measurements ( Average ) . Body Length  4.18 mm.  Body Width  0.627 mm.  Diameter Anterior sucker  0.095 mm.  Diameter V e n t r a l sucker  0.590 mm.  Diameter of C o l l a r  0.22® mm.  Identificationi The most obvious features i n common with the adult E.C. 1 echinostome and Echinoparyphium recurvatum are the number of c o l l a r spines and the body dimensions.  The arrangement of the c o l l a r spines  i s somewhat d i f f e r e n t i n the two worms, for Echinoparyphium recurvatum has four spines on each lappet, i n two pairs, whereas the adult form E.C. 1 has s i x lappet spines obviously paired.  The remainder of  the c o l l a r spines i n both worms are arranged i n two dorsal rows, with those i n the oral row smaller than those i n the aboral.  The folltfwing i s a-comparisoh of dimensions f o r the adult E.C. 1 and Echinoparyphium recurvatum ( from Dawes, 1946 ) . Adult from E.C. 1.  Echinoparyphium recurvatum  Body Length Body Width; No. C o l l a r Spines Lappet Spines  4.18 mm. 0.065 mm.  4^5 mm. 0.05 - 0.06 mm.  45  45  12  8  .;;  69.  Dorsal Spines  33  Egg Dimensions  3V  0.102 - 0.065 mm.  0.20.08 - 0.081 / mm.  Summary of L i f e Cycle Studies for E .C. 1: E.C. 1 was experimentally infected i n three species of snails. ella.  Physa occidentalis* P. c f traskjb and Pseudosuccinea colum-  An examination  of n a t u r a l l y infected s n a i l s revealed that  P. cf t r a s k i i i , Pseudosuccinea columella and Lymnaea proxima, contained -£©j=ty—M-ve- spined cysts i d e n t i c a l with those from E.C. 1. Tadpoles, c a t f i s h and goldfish were unsuccessfully exposed to E.C. 1. Rats, guinea pigs and ducklings were found to be unsuccessful as experimental adult hosts f o r t h i s c e r c a r i a .  E.C. 1 reached the adult  stage i n an experimentally infected pigeon.  The. cysts fed t o - t h i s  pigeon came from n a t u r a l l y infected snails collected at Burnaby Lake.  The cysts were morphologically i d e n t i c a l with those of E.C. 1.  The pigeon was proven t o be uninfected by trematodes p r i o r to the i n f e c t i v e feeding experiment.  On the basis of c o l l a r spine number  and arrangement, body dimensions and other morphological features, the adult worm has been i d e n t i f i e d as Echinoparyphium recurvatum.  Echinostome C e r c a r i a No. 2.  C e r c a r i a ! I n f e c t i o n Experiments: Experiments with Mollusca: Several species of uninfected, laboratory-raised snails were exposed, as described i n experiments with E.C. 1, to attack by  70.  E.C. 2.  Of these, Physa occidentalis and P. cf t r a s k i i were un-  successfully^infected.  Pseudosuccinea columella and Gyraulus  vermicularis were unsuccessfully exposed to E.C. 2, but since the number_of cercariae used was small, the failure to infect can hot be regarded as evidence of immunity. Experiments with Vertebrates; Two tadpoles taken from Burnaby Lake were exposed to attack by E.C. 2.  These animals were examined three weeks later and were  found to contain several echinostome cysts. The exact number of collar spines and flame cell formula i n these cysts was d i f f i c u l t to determine, however the size agrees very favourably with the size of the  cysts experimentally infected from E.C.-2. I t must be noted  that since the tadpoles cannot be regarded as uninfected, the success of the infection experiments i s i n doubt. The indication i s , -though, that the tadpoles of Burnaby Lake do act as second intermediate hosts t o E *C. 2. Metacercarial Infection Experiments. As i n the metacercarial infection experiments described for E.C. 1, several animals were selected as possible adult hosts for E .C. 2 and fed cysts either v i a medicine dropper or i n drinking milk. A l l these experiments, using the cysts identified as the encysted stage of E.C. 2, were unsuccessful. This undoubtedly was due i n some instances to an insufficient number of cysts being used, and i n others, to what may have been natural immunity of the host.  71. A l l these experiments were carried oui as described i n the experiments for E.C. 1. -For the aake of brevity i t may be stated here that pigeons, ducklings, guinea pigs and albino fats were unable to be infected with the metacercariae of E.G. 2. Summary of Life Cycle Studies with E.C. 2. 1st Intermediate Hosts: None of the miracidial -infection experiments involving E.C. 2 were sudcessfuly However, three species of snails from Burnaby Lake have been found to be naturally infficted with E.C. 2. These snails are — pseudosuccinea columella.PhVsa occidentalis and Helisoma t r i v o l v i s . 2nd Intermediate Hosts: Physa occidentalis and P. cf traski have been found to be 2nd Intermediate hosts for B.C. 2.  Pseudosuccinea columella, P cf  t r a s k i l and P. occidentalis have been found to be naturally infected second Intermediate hosts for E.G. 2. Adult Hosts: None of the experimental adult hosts were successfully infected.  The negative results are possibly due to improper diet,  or more probably, to the fact that too few number of cysts were fed to to the animals.  EXPLANATION OF PLATE V I I I . Echinostoma revolutum.  Fig. 1 —  Sketch of adult worm from hand lens showing some of the s t r u c t u r a l d e t a i l s ,  x 10.  F i g . 2 — Ventral view of anterior end showing arrangement of c o l l a r spines, x 200. Fig* 3 —  Adult worm, actual s i z e .  F i g . 4 — L a t e r a l view of anterior end showing lappet spines,  x 200.  F i g * 5 — Camera l u c i d a drawing ( low power ) of developing piracidium. F i g * 6 — Mature miracidium within egg. Camera l u c i d a drawing, high power.  PLATS V I I I .  72. I d e n t i f i c a t i o n of Adult Stage of E.G. 2»  On morphological ©rounds at l e a s t , -the adult stage Of E.C .2 i s undoubtedly Echinostoma revolutum found i n the muskrat of Burnaby Lake.  As previously stated ( Page 35 ), E .G. 2 i s decidedly similar  to Cercaria echinostomum revolutum as described by Beaver ( 1937 ) . On these grounds the linkage with E . revolutum appears conclusive, for as Beaver ( 1937 ) concludes  i n his monumental work on t h i s  trematode " the Qercaria resembles the adult so Closely i n cephalic spination that positive i d e n t i f i c a t i o n s can. be made from t h i s character alone."  Xiphidiocerearia No. 1.  C e r c a r i a l I n f e c t i o n Experiments; Experiments with Mollusca. 1. ) Two large uninfected P. occidenialis were exposed for 24 hours to approximately f i f t y X.C. 1., which emerged from a large Lymnaea p a l u s t r i s .  The snails were crushed and examined 9  days l a t e r but did not contain metacercariae. 2. ) A large laboratory-bred uninfected Physa cf t r a s k i i was placed i n an, aquarium containing a L . proxima shedding large numbers of X.C. 1.  The uninfected s n a i l remained exposed to the  cercariae f o r 10 days, after which time i t was removed from i t s s h e l l and thoroughly examined under low power magnification. encysted cercariae were found.  No  •  • • r.  73..  3.) Two uninfected P. occidentalis and one uninfected Pseudosuccinea columella were exposed to large numbers Of X.C. 1 for 2 days.  These snails were then kept i n an aquarium f o r 6 weeks,  following which they were teased and examined.  No cysts were found  i n any of the s n a i l s . .- 4.) An uninfected Menetus cooperi was exposed to 16 X.C. 1 i n a Syracuse d i s h .  A f t e r 2 days the s n a i l was removed t o an aquar-  ium and kept f o r 3 weeks.  No cysts v/ere found when the s n a i l was  crushed and examined. Experiments with C a t f i s h - -  On two instances, two small, c a t f i s h aaken from Burnaby Lake were placed f o r 48 hours i n an aquarium with a large L . p a l u s t r i s from which large numbers of X.C. 1 were emerging d a i l y .  One  month a f t e r exposure these f i s h were k i l l e d and thoroughly examined externally and i n t e r n a l l y .  No metacercariae were found.  Experiments with Goldfish:  . Approximately 300 X.C. 1 were added f o r three successive days t o an aquarium containing a medium si. zed goldgish.  Two weeks  later the. f i s h were k i l l e d ard a thorough examination made. No cysts were found.  Experiments with Gammarus sp t A$k gammarids used i n these experiments were considered free of i n f e c t i o n by trematodes after an examination of 30 specimens  •  7 4  taken from a l i l y pond showed no cysts were present.  1.) Three gammarids werepplaced i n an aquarium with a. large L. p a l u s t r i s shedding large numbers of X.C. 1. day these amphipods were found dead.  On the second  An examination revealed no  metacercariae. 2. ) Four,additional gaarmarids were placed intthe same aquarium as No. 1 f  o  r  two days.  An examination of the crushed bodies  of the gammarids on the t h i r d day showed that no cysts were present. 3. ) Five gammarids were placed i n a large number of X.C. 1, being shedrlfrom a L. proxima. day of exposure.  Three gammarids were dead on the second  No cysts were found a f t e r a thorough examination  of these animals under low power magnification.  The remaining two  gammarids died the following day and i n each, four s t y l e t cysts were found.  As f a r as could be determined, these cysts were i d e n t i c a l  to the cysts found i n snails infected with X .C. 1.  One cyst was  found i n the f l e s h of a basal appendage segment. A l l other cysts, appeared t o be free i n the teased remains of the gammarid. 4. ) Three gammarids were placed i n an aquarium f o r three days, with large numbers of X.C. 1 shed from the L. proxima used i n No. 3.  On examination two days l a t e r each gammarid was found to con-  t a i n many s t y l e t cysts ( 35, 40 and 80 ) . Most of these cysts were located free i n the teased gammarids, but many were observed within the appendage segments. 5. ) Two gammarids. were added t o water containing a f a i r number of X.C. 1.  One was examined two days l a t e r and contained  75. a single c y s t .  .  The second gammarid yielded nine cysts, none of  which were i n the f l e s h of the appendages. A l l metacercaria showed movement.  Metacercarial I n f e c t i o n Experiments;  Experiments with Goldfish;  1. ) Eight s t y l e i c e r c a r i a taken from an experimentally infected s n a i l of the above O e r c a r i a l I n f e c t i o n Experiments were fed, v i a a medicine dropper, t o a large g o l d f i s h .  On the 14th day  following i n f e c t i v e feeding the f i s h was k i l l e d and examined. No trematodes were found i n intestines or v i s c e r a . 2. ) F i f t e e n to twenty s t y l e t cysts taken from experimenta l l y infected, gammarids were f e d to a small g o l d f i s h . Ten days a f i e r t h i s feeding the g o l d f i s h was k i l l e d and examined. No trematodes were found.  Duckling Experiments;  Nine s t y l e t cercariae were fed v i a medicine dropper to a duckling two days o l d . Thirteen days a f t e r i n f e c t i v e feeding, the duckling was s a c r i f i c e d and a thorough examination made of the viscera.  No adult worms were discovered.  Experiments v/ith Rats: 1.) Ten cysts taken from an experimentally  infected  Gammarus sp. were fed t o an adult albino r a t . Six weeks a f t e r feeding t h i s r a t was s a c r i f i c e d .  No trematodes were found i n an  76 ... examination of the intestines. 2.) Nine stylet cysts of G.X. 1 were fed to a small albino rat.  On the 34th day after feeding, the rat was killed and examin-  ed . No adult trematodes were found. Experiments with Guinea Pigs: Four X.C. 1 cysts taken from an experimentally infected gammarid were fed to a guinea pig, v i a medicine dropper. The animal was killed and examined 34 days after feeding. No trematodes were found i n i t s gut. Summary of Life Cycle Studies with X.C. 1. It would appear that the 2nd Intermediate hosts of X.C. 1 are specific.  Experimental encystment of X.C. 1 was unsuccessful i n  L. palustris L. proxima t  a  Menetus cooperi, goldgish and catfish.  A gammarus species was found to be an experimental 2nd Intermediate host for X.C. 1. No successful infections were made with X.C. 1 shed from L. palustris.  This may be the result of i n -  sufficient numbers of.cercaiiae used, the premature death of the gammarids, or the fact that the cercariae emerging from the L. palustris were not X.C. 1. Encystment i n gammarids appears to take place i n the body as well as i n the fleshy portion of the appendages. Mp emcystment was observed on the substratum.  Unsuccessful attempts  were made to infect goldfish, ducklings, rats and guinea pigs with the cysts of X .C. 1.  77 Xiphidiocercaria No. 2: Life cycle experiments were confined to the exposure- of a number of ininfected gammarus sp to attack by X.C. 2. -The experiments were performed as described for X.C. 1. On two occasions gammarids exposed to large numbers of X.C. 2 for two days contained 40 and 80 stylet cysts.  These metacercaria were not studied i n any  detail, but appeared to show much resemblance to those of X.C.I Furcocercous Cercaria No. 1: Several experiments were designed to determine whether or not F .C. §, develops as a tetracotyle i n a second intermediate host or i s directly infective to the adult host, either orally or cuiaheously. A l l snail's used as experimental hosts were laboratoryraised uninfected specimens.  The ducklings used were incubator  hatched. Gammarids, as i n previously described experiments were taken from aXlily pond and considered to beuuninfected.- The tadpoles and catfish were taken from Burnaby Lake, and could not be considered as uninfected. The animals were exposed to F.C. 1 by placing them i n 500 cc. of water i n an aquarium containing large numbers of the cercariae. Results of Experiments: Experiments with Mollusca. Physa occidentalis, P. df t r a s k i i , Pseudosuccinea colum-  76. e l l a were unsuccessfully exposed to F.C. 1. Experiments v/ith Gammarussp. — unsuccessful. Experiments-with Ducklings — unsuccessful. 1. ) The feet and legs of a four day old duckling which • had just died were immersed for three hours i n water containing a great number of F.C. 1. The tissue of the foot was then examined under low power for the presence of penetrating or penetrated cercariae.  No cercariae were found. The^tissue of the foot was then  teased and examined. No cercariae or tetracotyles were found. 2. ) A duckling was fed approximately  50 F.C.-l via drinking  water for a period on one week. This animal was prematurely and inadvertently destroyed by a predator three days after, oral feeding ceased. An examination could not be made before much of the blood had congealed, making perfusion experiments for the presence of blood parasites impossible.  The animal was exsagihated by decapit-  ation, and as much blood as possible was thoroughly examined. No flukes were found. Goldfish Experiments — unsuccessful. Summary of Life Cycle Studies with F.C. 1. Physa occidentalism P. cf t r a s k i i and Pseudosuccinea columella were unsuccessfully exposed to infectymn by X.C. 1. On one occasion, a Pseudosuccinea columella collected at Burnaby Lake was found to contain eight large cyst-like objects, which showed much resemblance to the tetracotyles of strigeid cercariae. .There  i s , then, evidence that the Burnaby Lake s n a i l s do act as natural hosts f o r tetracotyles of s t r i g e i d cercariae, to which group E.C. 1 belongs.  - Tadpoles and c a t f i s h also taken from Burnaby Lake contained strigeid-like tetracotyls.  Thus, although i t has not been supported  by experimental evidence from t h i s i n v e s t i g a t i o n , there are i n d i c ations that the s n a i l s , tadpoles and c a t f i s h of Burnaby Lake harbour tetracotyles of s t r i g e i d trematodes, one of which might be F .0. 1.  Gammarus sp, ducklings and g o l d f i s h apparently do not serve as hosts f o r F.C. 1.  Furcocercous Cercaria No. 2. Similar experiments as those f o r F.C. 1 were c a r r i e d out using F.C. 2.  The r e s u l t s of these experiments are presented here  i n b r i e f form.  Experiments with Molluscs: Three Physa sp were exposed to F.C. 2 f o r periods of one, three, and 11 days r e s p e c t i v e l y .  No l a r v a l trematodes was found  when the s n a i l s were crushed and examined. Experiments with Tadpoles: A tadpole taken from Burnaby Lake was exposed to F .C-. 2 shed from L . p a l u s t r i s f o r a period of 22 hours. the tadpole was teased and examined. found.  Two weeks l a t e r  No l a r v a l treaatodes were  80. Experiments with Goldfish* A large g o l d f i s h was exposed to F.C. 2 f o r three days, after which i t was crushed and examined under low power.  No l a r v a l  stages were found. Experiments'with. Ducklings $ A two day old duckling was fed 30 or 40 cercariae i n 200 c c . of drinking water.daily f o r one week.  On the eleventh day  the animal was examined f o r flukes i n the blood and v i s c e r a . No l a r v a l stages were found•  Summary of L i f e Cycle Studies with F.C. 2» S n a i l s , tadpoles, g o l d f i s h and ducklings serve as experimental hosts f o r F.C. 2.  The number of  experiments undertaken :  p r o h i b i t these negative r e s u l t s from being regarded as conclusive.  81. SCHISTOSOME DERMATITIS EXPERIMENTS.  INTRODUCTION' Schistosome dermatitis i s a skin infection i n humans oar-r-ied by the penetration of the cercariae of avian trematodes. I t i s common i n north and central United States andGCanada, and i s popularly called "swimmer's itch," or " swimmer's fash."  In many  instances a severe dermatitis results -from exposure to these cercariae.  However laboratory experiments have shown thai ihe penetration  i s otherwise harmless, proceeding only a short distance before the cercariae die. Cort ( 1928 ) was the f i r s t worker i n America io demonstrate experimentally ihat non-human schistosome cercariae could penetrate human skin and cause papular eruptions. He found four furcocercous cercariae responsible for this dermatitis i n Michigan, all'belonging to the C. elvae group.- Several years later, Cori ( 1936 a J ( 1936 b ) presented a comprehensive review of ihe work up to date on schistosome dermatitis i n America. This was followed by several pertinent papers by Cort and.his associates Cort ( 1936 b ), Talbot ( 1936 ), Sort and Talbot ( 1936 ) and _ B.rackett ( 1940 ) ( 1941 ). The most recent reports on the subject are by MacMuHen and Meaver ( 1945 ), Macf arlane and Macy ( 1946 ), Olivier ( 1947 ), and Hunter et a l ( 1949 ) . Although these worms are harmless to humans, the possibil-  821 i t y that t h e i r intermediate  hosts might be the intermediate  hosts  to human schistosomes also has interested at l e a s t one worker. Stunkard ( 1946  ) tested the p o s s i b i l i t y of the AmericaliJSpecies  of  s n a i l s acting as hosts to the cercariae of human schistosome flukes commonly found i n A s i a and t r o p i c a l l a t i t u d e s . He exposed representative specimens of the-more common and r e a d i l y available s n a i l s from eastern.United  States to the miracidia of human schistosomes.  Among the s n a i l s used were L . pajbustris.- Pseudosuccinea columella. Physa-spp. H. t r i v o l v i s and H. anceps, which are to be found at Burnaby Lake. experiments.  No p o s i t i v e r e s u l t s were obtained i n any of these Stunkard states that " the f a i l u r e to obtain cercariae  i s not s u r p r i s i n g since i t i s d i f f i c u l t to Consummate w e l l known trematode l i f e cycles under laboratory conditions, even when natu r a l intermediate  hosts are employed."  He suggests that these neg-  ative r e s u l t s are fiar from being conclusive,and  may  lead to a f a l s e  sense of s e c u r i t y about l o c a l species of s n a i l s beingiimmune to human schistosomes.  U n t i l McLeod s ( 1934 ,:  ) work appeared a l l c c e r c a r i a e caus-  ing schistosome dermatitis were apparently  of the apharyngeal b r e v i -  furcate distome cercariae of the C. elvae,group, that i s , t y p i c a l members of the Schistosomatidae. McLeod discovered two ;  sides that of C. elvae M i l l e r , 1923, which produced swimmer's i t c h .  species, be-  from Clear Lake, Manitoba,  These cercariae are members of the  Strigeidae (pharyngeal longifurcate distome cercariae ) and named C. Wardlei McLeod, 1934  and C. fcajkovi, McLeod,  1934.  83. Swales ( 1936  ). working i n the same Clear Lake, Manitoba,  found C. elvae M i l l e r , 1923  and a Cercaria sp i n Stagnicola  emarginata Canadensis ( Sowerby ) causing dermatitis, along with f i v e species of S t r i g e i d cercariae, I' none of which indicated any power of penetration onto the human skin."  Methods:  Two  experimental human hosts were used i n the experiments  with F.C. 1 and F.C. 2, one a student-co l i e ague ( Host-1 ), the other the author ( Host 2 ) .  Two  procedures were adopted, one  c a l l e d the Drop Method and the other the Immersion Method. 1.  Drop Method;  This method consisted of placing a drop of water containing the or more cercariae on. the f l e x o r surface of the forearm. This r e l a t i v e l y h a i r l e s s portion of the arm allows for more s e n s i t ive reactions than other skin surfaces.  The drop of water was  allowed to stand for a c e r t a i n period and then shaken off and a i r dried.  Each drop of water was  ringed with i n d e l i b l e ink.  In removing the cercariae from the aquaria^a medicine dropper was u t i l i z e d . that when i t was  As l i t t l e water as possible was  taken up so  expelled, the dropsjof water formed on the skin  surface would not be so large as t o e a s i l y r o l l o f f . expelling the drops on the arm, the dropper was  Just p r i o r to  held before a beam  M. of l i g h t i n order to check the number.of cercariae contained and to. make c e r t a i n that none had-become attached t o the s i d e s .  Both the  furcocercariae experimented with here were found to become r e a d i l y and stubbornly attached t o the inside of the medicine dropper. I t was  thus found advisable t o make the time between sucking up the  cercariae t o placing the drop of water on the arm as short as possible .  Several of these drops of water containing active cercariae were placed along the length of the arm, each one ringed with i n delible ink.  The arm was held steady and the drops l e f t  undisturbed  for periods up to an hour i n length, then the water was shaken off and the infected areas allowed to a i r - d r y . Notes were made on any subsequent sens&iions experienced  and skin reactions observed.  Drops of water containing no cercariae were placed on the f l e x o r surface of the other arm i n order thataa comparison could be made of c e r c a r i a l and non-cercarial water.  2.  Immersion Method; The second method consisted of placing the elbow or f l e x o r  surface of the wri&t i n a stacking dish, or a p e t r i dish, containing a large number of the active cercariae.  The corresponding  surface ct'  the other arm was immersed i n an equal- quantity of water with|ao cercariae . The  skin surface v/as kept i n the water f o r a.,pefiod of  f i v e minutes, then removed and allowed to dry.  This was then followed  85. by separate immersions of 10 and 25 minutes,.each followed drying period.  by.a  In thisjnanner, the peaiodic immersion and drying Of  a person while swimming was simulated, representing the conditions under which actual or natural, c e r c a r i a l attack i s made.  Results and Discussion of Infections  Furcocercaria No. I •  Several attempts, using both the above metikods, wefee made to produce dermatitis using t h i s cefCaria^l. periments on either host was  successful.  None of the  ex-  I t seems very l i k e l y ,  to t h i s worker at l e a s t , that F.C. 1 i s not a dermatitis -producing schistosome.  Furcocercaria No.  2.  Drop Method: Case No.,1  (-Colleague ) .  Three drops of water containing one or more cercariae each were placed on the f l e x o r surface of the r i g h t arm. drops without  cercariae were placed on the l e f t arm.  Several  A slight  i t c h i n g sensation and intermittent sharp pricks commenced within 15 minutes. a half.  This " p r i c k l y heat f e e l i n g " stopped within an hour and  One hour a f t e r exposure, three small erythematous spots,  were observed. i n diameter.  By seven hours these red areas had increased to 2  No further i t c h i n g was  experienced.  At twenty hours  the erythema had become more d i f f u s e , extending now t h 3 mm. diameter.  At t h i s stage the spots were d e f i n i t e p&£v&es with  in  mm.  1  86.  minute white heads. Erythema decreased after 24 hours. a l l trace of the i n f e c t i o n had disappeared.  By 48 houfes  No such reaction was  observed i n the l e f t arm.  Case No. 2.  (Colleague ) .  Seven drops of water, each containing one.or two cercariae were placed on the flexor surface of the r i g h t forearm.  Approximat-  ely 15 minutes l a t e r a p r i c k l i n g sensation was experienced.  Itch-  ing became intermittently more intense but did not r e s u l t i n pruritus.  After h a l f an hour, the drops were shaken o f f and allowed  to a i r - d r y . served.  At t h i s time seven small erythematous  areas were ob-  These were sharply defined areas 1mm. i n diameter.  The  s l i g h t i t c h i n g ceased a f t e r about an hour and was not experienced again.  Two hours after exposure, the erythema had increased t o  1.5 mm. i n diameter.  At 22 hours, pink papules appeared, and at  28 hours these papules measured three mm. i n diameter and.about 1.5 mm. high.  By the second day the papules had become p a l e .  the t h i r d day a l l skin reaction disappeared.  On  No reaction was ex-  perienced i n the l e f t arm.  An interesting.reaction i n t h i s case appeared three weeks later.  At spots on the arm, which, as f a r as could be determined,  were i d e n t i c a l with the o r i g i n a l l y papulated areas, nev; small red papules appeared. meter.  These raised areas developed t o 1.5 mm. i n d i a -  No i t c h i n g or t i n g l i n g sensations were experienced.  new areas remained obvious f o r seven days.  These  87. Case No. 3. ..( Author ) . - Seven drops of water, each containing one or more F.C. 2 were-placed on the f l e x o r surface of the l e f t arm.  Several Control  drops were placed on the r i g h t arm. .The- drops were l e f t on f o r ten minutes and then shaken o f f .  No reactions whatsoever were experienc-  ed.  Case No. 4.  ( Author ) .  Seven drops of water containing one or more F.C. 2 were placed on the flexor surface of the l e f t arm and allowed to remain for t h i r t y - f i v e minutes. to a i r - d r y .  The drops were then shaken o f f and allowed  A strong pruritus commenced i n two or three of the  exposed areas after t e n minutes.  In t h i r t y minutes, four erythemat-  ous spots were observed i n as many ringed areas.  Intense i t c h i n g i n  and around these areas was experienced at t h i s time. creased after an hour but the,number of erythematous creased t o s i x , each approximately 2mm. i n diameter. p r u r i t i s developed. become papular.  Itching deareas had i n No further,  At 20 hours following exposure, the spots had  At 24 hours the papules had become-very prominent  and had begun t o disappear at 30 hours.  On the second day, erythema  was less l o c a l i z e d , each area now extending 4 or 5 mm. i n diameter. Papules were present but not obvious; a s l i g h t pain was experienced., when they were touched, otherwise no sensations were f e l t .  Erythema  remained f o r about two weeks as small unraised areas on the skin, about 1.5 mm', i n diameter.  88. Case No. 5 ( Author ) .  This experiment u t i l i z e d the same arm surface as i n Case No.-.4 and was  started three days after the drops i n Case No. 4  were placed on the arm.  Eight additional drops of water containing  one or more cercariae were placed near the previously infected areas. Within ten minutes intense i t c h i n g began i n one area very close to a previously papulated area. oped i n t h i s new minutes.  area.  Five separate erythematous spots devel-  Erythematous macules appeared i n t h i r t y  At 35 minutes i t c h i n g was  almost unbearable.  The drops  were shaken off at 45 minutes, at which time three red spots were present.  Itching continued f o r one hour.,.  small red areas could be seen.  B  y  x y%  hours, f i f t e e n  One area of f i v e spots  developed  i n t o a common raised welt about 2 cm. i n diameter. On the 3rd day, some of the papules were purposely i r r i t a t ed.  Within twenty-four hours these had become very s l i g h t l y pustular,  with a small scab on t h e ^ u r f a c e .  These minute pustules remained  obvious f o r a week, during which time there was ance of the erythema.  a gradual disappear-  The small scars remained evident f o r s i x weeks.  Immersion Method; Of several attempts t o produce dermatitis using t h i s method only once was there any thing more than s l i g h t i t c h i n g experienced by either host.  This i t c h i n g was only s l i g h t l y more  intense than the " t i n g l i n g " sensation induced i n the areas immersed i n non- c e r c a r i a l water.  89. Summary of Results of Laboratory Exposure to F .C. 2.: Colleague; Slight itchinga&t 15 minutes.. No intense i t c h i n g or p r u r i t u s . Itching ceased a f t e r 1 1/2 hours. Erythematous macules at 30 min., decreased a f t e r 28 hours; maximus papulation at 24 hours. No pustule development. Skin reaction disappeared i n 3 days. Author:  ( In general reactions more acute than, i n colleague). Extreme i t c h i n g and p r u r i t i s at 10 min., continued for 1 hour. Erythema macules appeared at 30 min. S l i g h t i t c h i n g a f t e r 1 1/2 hours. Papules developed t o maximum by 24 hours, remaining f o r three days. Erythema l a s t i n g two weeks. Welts, pustules and intense erythema i f i r r i t a t e d .  Conclusions: 1. ) F.C. 2 i s capable of producing Schistosome dermatitis. 2. ) There appears t o be a difference i n host reaction to the penetration of F.C. 2. 3. ) The i n t e n s i t y of the r e a c t i o n i s increased i n proportion to the number of i n f e c t i n g cercariae. per unit area. 4. ) Pustulation and scar tissue r e s u l t i f the papules are  90.  irritated.  -j  y  5.) The strigeid cercaria F.C. 1 i s apparently incapable of producing a dermatitis i n humans.  ,91. E c o l o g i c a l Relations of Larval Trematodes of Burhahy Lakes  In t h i s discussion of the degree of l a r v a l trematode i n f e s t ation i n B urnaby Lake s n a i l s i t i s considered  to be of Value to  preface the findings with some remarks on the c o l l e c t i o n areas-themselves, and also upon the snail.populations found.  Since the s n a i l s  that were examined in.the laboratory were taken from d e f i n i t e  areas  of Burnaby Lake, i t was hoped that i n addition to determining the degree and species.of i n f e c t i o n , that the i n v e s t i g a t i o n might.disclose possible area differences which exist i n the s n a i l fauna and t h e i r l a r v a l trematodes.  C o l l e c t i o n Areas at Btarnaby Lake ( Plate X ) . Three shore areas of Burnaby Lake from which s n a i l c o l l e c t ions were made were selected on the basis of e c o l o g i c a l differences and a c c e s s i b i l i t y .  Although the lake i s small, and thus the c o l l e c t -  ion areas not f a r removed from each other, i t was f e l t that the areas chosen represented s u f f i c i e n t differences i n habitat to warrant observations  being made f o r the p o s s i b i l i t y of £auna d i f f -  erences .  In general, Burnaby Lake area i s a t y p i c a l marsh and bog. area, with marsh and. mud shores bordering the lake,proper.  It is a  Proyincial.Game Reserve and as such harbours a large muskrat popu l a t i o n , large numbers of migratory water fowl at various times of the year, and many other vertebrates, resident and migratory, which are possible adult trematode hosts.  92. 1.) Laut Park Area.  This area i s on the north side of Burnaby Lake, at the base of Burnaby Mountain. - I t i s reached by means of the Laut Pakk Road which follows the course of a small clear water stream entering the lake on t h i s north shore. The bulk of the snails taken from t h i s area were collected from approximately two hundred feet of shore l i n e to the west of the mouth of the Laut Park stream.  The shore here varies from a sand  and gravel d i s t r i c t near the stream mouth to a muddy shore with much decaying vegetation at the western extremity... Host of the snails were  collected from the surface of the mud and shallow shore  pools and offshore marshes.  2.) S t i l l Greek Area.  C o l l e c t i n g i n this area was confined' to the region around the mouth of S t i l l Creek, at the western-most end of Burnaby Lake, and along the creek banks f o r a distance of f i v e hundred feet from tho l a k e .  The banks of t h i s creek are of hard clay or mud  and  bordered by c a t t a i l ( Typha l a t i f o l i a ), rushes ( Juncus sp ) and bent grass ( agrostis ) .  Most of the snails were c o l l e c t e d from  the leaves of the rushes,and grasses bent over and submerged at the creek's edge.  Some s n a i l s were also collected from the  surface at the mouth of S t i l l Creek.  3.) Deer CreekiAreat  mud  93. 3 .) Beer Creek Area;  Collections i n t h i s area were made i n the v i c i n i t y of the mouth of the- stream which connects Deer Lake with Burnaby Lake. This i s the largest of the shore areas from which c o l l e c t i o n s were made. Snails were taken from the shore of the lake extending both east and west of Deer Creek mouth, but p r i n c i p a l l y i n the eastward d i r e c t i o n f o r a distance of approxiteately 200 f e e t .  This area i s  t y p i c a l f r e s h w a t e r bag.  Rushes and bent grass border the lake-and  the banks of Deer Creek.  Most of the s n a i l s were collected from,  the surface of the moist mud  and decaying vegetation, and i n shallow  bog pools of the offshore regions.  The l i m i t s of a l l these areas are shown i n Plate X.  Snails Found at Burnaby Lake ( S e e Plate IX  }.  The following i s a l i s t of the s n a i l species collected at Burnaby Lake as i d e n t i f i e d by Dr. Henry van der Schalie, of the University of Michigan. Pseudosuccinea columella  ( Say )  Lymnaea proxima rowelli- ( Tyron ) Lymnaea p a l u s t r i s  ( Muller )  Helisoma t r i v o l v i s h o r n i i ( Tyron ) Helisoma anoeps ( Menke ) —  formerly c a l l e d antrosum .( Conrad ) .  Menetus cooperi ( F . C . Baker ) — formerly c a l l e d planulatus ( Cooper ) .  EXPLANATION OF PLATE IX. Snail Species collected at Burnaby Lake. 1. -2.  Pseudosuccinea columella ( Say ) Lymnaea palustris ( Muller )  3* Lymnaea proxima rowelli ( Tyron ) 4. Helisoma trivftlvis hor'nii ( Tyron ) 5. Helisoma anceps ( Monke ) 6. Me^etus cooperi ( F .C. B aker ) 7.  Gyraulus vermicularis ( Gould )  8. Physa occidentalis ( Tyron ) 9. Physa cf traskii ( Lea )  94. Gyraulus vermicularis ( Gould ) Physa occidentalis ( Tyron )  -  Physa cf . t r a s k i i ( Lea ) — may be only a form of Physa occidentalis ( Tyron ) . Perrissia caurina ( Cooper ) . Collection Areas and their Snail Populations: Tables No. I, I I , and-III give data on area differences at Burnaby Lake, both of the snail host populations and their larval trematode infections. From these tables the following generalizations have been taken. 1') Laut Park Area: In the number of snails collected and examined, this area heads the other two. However, most of the snails collected were of one species, Pseudosuccinea columella, so that the number examined gives no indication of the richness Of the wiolluscan fauna. PseudoauCoinea columella were mostly found on the mud shore when the water level of the lake was low, as well as i n small water-filled depressions, and on moist duckweed and decaying vegetation.  These snails were found throughout the year. During  December, January and February, this species was the only one found in any quantity i n the area. In the ice and snow free sections of the shore Pseudosuccinea columella was usually found on the undersurface of objects lying i n the mud.  95. The species found i n next great/abundance were the two Physas —  Physa occidentalis and P. c f t r a s k i i .  A t o t a l of 102  of these two species wer^e- collected and examined as compared with about 200 Pseudosuccinea columella. Lymnaea proxima and L . p a l u s t r i s were found i n small numbers ~ taken from the area.  only three and one respectively being  One Helisoma- t r i v o l v i s was c o l l e c t e d .  Very  few of the inconspicuous Gyraulus vermicularis were taken, although they appeared t o be present i n large numbers on the mud surface here. No Helisoma anceps or F e r r i s s i a caurina were collected at Laut Park.  However, the collections were i n no way exhaustive and  there appeared no reason why t h i s species cannot be found i n t u i s habitat.  2.  S t i l l Creek;  During the warm late spring and summer months^Large quantities of snails were found i n t h i s area. specimens were collected creek.  The majority of  from submerged rushes at the edte of the  Many were found f l o a t i n g at the water surf ace- near the  creek banks.  Great quantities of the gelatinous egg masses are  attached t o the submerged vegetation. By l a t e August, the number of snails to be found i n t h i s area f e l l o f f sharply. No s n a i l 6 i n any appreciable quantity could be found i n t h i s area from l a t e Oct ober t o A p r i l .  Physa spp«and Pseudosuccinea columella we re i n  greatest concentration i n t h i s area. Although very few snails from t h i s area were examined f o r  96.,  larval trematodes, i t was found that during the.summer months i i harboured more specimens than the other two areas. 3 .) Dear Creek: This area was found to have the most bountiful molluscan. fauna.  In contrast to Laut Park Area, Deer Creek was without pseudo-  succinea columella during winter months. Phyaa occidentalis was in greater abundance during the summer nonths. L. proama, L. palustris . and a. irivolvis.were collected during .all seasons at Deer Creek-but in relatively small numbers. During the winter season these species could be found on the surface of the mud and amongst duckweed. Pseudosuccinea columella. Physa SPP are in large supply ©a the under surface of the pond l i l y ( Mymphea polysepala ) which a l most completely covers the lake surface during late spring and summer. Egg masses are also plentiful on; the under surface of this plant. Summary of Area Differences im Larval Trematode Infection: The percentage infection by eaoh larval stage ia given in Table III. The three collection areas at Burnaby Lake are no great distance apart and yet appreciable differences in the degree of larval trematode infection of their snails has been shown to exist. A total of five hundred and sixty-two snails were examined in the laboratory for the presence of cercariae and other intramolluscan  EXPLANATION OF PLATE X.  Map of Burnaby Lake showing C o l l e c t i o n Areas. Shaded portions indicate regions from which collections were made.  A.  Laut Park Area.  B.  S t i l l Creek Area.  C.  Deer Creek Srea.  97.  stages. Laut Park snails are the least parasitized by cercariae, rediae and sporocysts, but were found to be most heavily infected with the cyst stage. One percent of a l l snails examined containing cercariae and other intramolluscan^were collected at Laut Park, as compared to-two percent and seven percent from.Still Creek and Deer Creek respectively. Deer Creek also possessed the greatest number of species of cercariae. No xiphidiocercariae were found in snails collected at Laut Park and S t i l l Creek. Furcocercous cercariae were found in greater percentage in snails of a l l three areas than were the Echinostome and Xiphidiocercariae. These area differences can in no way be regarded as rigid. The number of snails examined from each area i s too small, and the survey was for one year only, so that definite conclusions cannot be made from the data.  Discussion of High Degree of Infection at Deer Creek: The Deer Creek area appears to be the most favourable for infection of snails by miracidia. This may be due to the cambinationi of the area having a greater year round abundance of snails and a large adult host population from which the infection of these snails can arise.  .  ._  98.  Hb accurate data on the distribution of muskrat or other non-avian hosts within the Burnaby Lake area has been taken. Observations that were made in this regard indicate that the Deer.Creek area is more heavily populated by muskrat than either the Laut Park or S t i l l Creek areas. This was determined by the number of muskrat actually seen, the number of defecating posts found, sedge cuttings and other typical signs of a muskrat population. During migratory seasons, waterfowl, were seen in great numbers on Burnaby Lake. Although the actual distribution of the birds among the three areas was impossible to determine, i t was noted, that signs of birds predominated in the Deer Creek area. On most occasions the shoreline here was noticeably marked by avian faeces and scored by bird tracks. This area appears to provide an excellent feeding iround for water fowl, especially when the water level i s low and much muddy shoreline is laid bare. A large vertebrate population such as may be found in the Deer Creek: area means a large quantity of trematode eggs being passed with the faeces into the lake water and moist shore.  Subsequently  a large number of the infective miracidia developing from these eggs are liable to cause a high percentage of infection in the snails of the area. Degree of Larval Trematode Infection in Burnaby Lake Snails: The following is a l i s t of the snails collected and their percent infection by a l l intramolluscan stages,  99.. Helisoma trivolvis  92$  Physa occidentalis  73$  P. cf traakii  70$  Lymnaea palustris  38$  Pseudosuccinea columella  27$  Menetus cooperi  26$  L. proxima  24$  ff. anceps  0$  Gyraulus germicularis  0$  Snail Species and their Infections See Tables I, I I . 1.) Helisoma t r i v o l v i s .  Only 12 of thes species were examined.  Eleven were infected by one stage or another of the larval  trematodes.  The majority of these snails came from Deer Creek ( See Table I ) and were for the most part infected by xiphidiocercariae.  Echino-  stome and furcocercous cercariae were also found i n this species of r  snail.  Summary of Larval Trematode Infection i n 12 H. trivolvis ( 92$ infected ). Number  Larva  Percent Infection  1  E.C. 1  9$  4  X.C. 1  33$  1  X.C. 2  9$  3  .P.O. 1  25$  100. 2  Echinostome cysts  1  Large u n i d e n t i f i e d cyst ( tetracotyle? )  2.) Physa o c c i d e n t a l i s .  17$ 9$  The l a r v a l trematode i n f e c t i o n  i n t h i s s n a i l was found t o be almost i d e n t i c a l with -that of P. c-f. traskii.  Dr. vandder Schalie i n h i s i d e n t i f i c a t i o n of the Burnaby  Lake s n a i l s , suggests that these two species may be one and the same thing, which may p a r t l y explain the s i m i l a r i t y i n i n f e c t i o n . One hundred and f o r t y specimens were examined and found t o be 7S$iinfected by l a r v a l trematodes*  The echinostome and furcocercous  were present i n equal degree.  cercariae  No Xiphidiocercariae were found i n -  f e c t i n g these-fonus. -As regards area differences ( See Table I ) an equal quantity of s n a i l s from Deer Creek and S t i l l Creek was i n :  fected.  Two s n a i l s only from Laut Park harboured l a r v a l f l u k e s , both  infected w i t h E .C. 1.  This a n a i l v a r i a b l y contained  metacercariae ( 44$ i n f e c t e d ) .  echinostome  Musfeldt ( 1945 ) found a s t y l e t and  p o s s i b l e non-stylet cercariae i n t h i s species at Burnaby Lake.  Summary of L a r v a l Trematode I n f e c t i o n i n 140 P. o c c i d e n t a l i s (' 73$ infected ) .  Number  Larva-  Percent I n f e c t i o n  6  E »C . 1  4$  2  E.C. 2  1$  6  F.C. 1  .*- 4$  2  F.C. 2  - 1$  •  101 ,  67  Echinostome cysts  48$  17  Large u n i d e n t i f i e d cysts  14$  3.) Physa c f . t r a a k i i .  Fifty-seven specimens were examined  and found to be 70$ infected by s i x probable i n f e c t i n g - s p e c i e s . xiphidiocercariae were found  Ho  .  Summary of L a r v a l Trematodes i n f e c t i n g 57 P. c f . t r a s k i i ( 70$ i n fected )... Number  Larva  Percent i n f e c t e d .  3  E.G. 1  5$  1  E.C. 2  2$  3  F.C. 1  5$  2  F «G. 2  25  -  3$  Echinostome cysts  6  44$  Unidentified cysts ( Tetracotyles?) 4.)  Lymnaea p a l u s t r i s .  greatest percentage.  Xiphidiocercariae-were  15$  present i n  The numbers of specimens examined was too  small to permit generalizations t o be made regarding or immunity e x i s t i n g in. these s n a i l s .  area differences  Only one specimen was taken  from Laut Park and S t i l l Creek, neither of ushich were i n f e c t e d . R e l a t i v e l y few. echinostome cystg were found.  102 Summary of L a r v a l Trematodes i n f e c t i o n i n 24 L . p a l u s t r i s ...... ( 38$ infected ).  Number  Larva  Percent i n f e c t e d .  2  E «C. 1  8$  1  X.C. 1  4$  1  F..C. 1  4$  3  Echinostome Cysts  1  Unidentified cysts  5.) Pseudosuccinea columella* were collected at Laut Park,. fected, by a F.C. 1. infected by a E .0. 1.  13$ 8$  The majority of t h i s , species  Only one of these specimens was i n -  Only, one from S t i l l Creek was found to be No xiphidiocercariae were found i n these  snails • In general, l a r v a l trematode i n f e c t i o n i n Pseudosuccinea columella was r e l a t i v e l y small; of two hundred and f i f t y - n i n e s n a i l s examined, only f i v e were foiund infected by cercariae.  The i n f e c t -  i o n by c y s t i c stages i n t h i s species was of a high degree.  Of two  hundred and fifty-two Pseudosuccinea columella examined s p e c i f i c a l l y f o r metacercariae, f i f t y - f i v e contained cysts i d e n t i f i e d as belonging to Echinostomes, while i n twelve specimens large u n i d e n t i f i e d cystB were found.  Of a l l species examined t h i s proved l>o be l e a s t  i n f e c t e d — 2$ ( See Table IV J by cercariae, and 27$ by both cercariae, and metacercariae.  . ,s  :  ,  •-  •;•  103.  r  Summary o;f Larval Trematode, Infection i n 259 Pseudosucdinea columella ( 27$ infected ). Number  Larva  Percent Infected.  I  E .0. 1  0.4$ i  1  E.C. 2  0.4$  1  F.C. I  0.4$  •31  F.C. 2  0.4$  55  Echinostome cysts  21 $  13  Unidentified cysts  5$  6. ) Henetus cooperi.  Of twenty-seven specimens examined. 26$  were found to be infected by echinostome cysts.- NO'cercariae of any species were observed i n this snail.  The infected snails were  collected at S t i l l Creek and Deer Creek. Summary of Larval Trematode Infection i n 27 Menetus cooperi ( 26$ infected. Number 7  Larva  Percent Infected  Echinostome cysts  26$ .  7. ) Lymnaea proxima. Thirty-five snails were examined, the majority of which were collecte at Deer 0reek. One specimen only r  came from S t i l l Creek and was uninfected.  Twenty-one percent of the  snails were infected with four cercariae species.  Nine snails  were so infected, dounting.all types of cysts, there were six probable infecting larval trematode species i n L. proxima,(See Table IV).  . .  -  , ...  -  104.  Summary of L a r v a l Trematode I n f e c t i o n i n 35 L . proxima (' 24$ infected ) . Number  Larvae  Peroent I n f e c t i o n  4  E.C. 1  11$  2  X.C. 1  6$  1  F.C. 1  3$  1  F.C. 2  3$  4  Echinostome cysts  11$  1  Unidentified cyst  3$  8) . Helisoma anceps.  Only three H. anceps we re examined.  specimens were found infected by l a r v a l trematodes.  No  A l l specimens  examined came from Deer Creek.  9..)- Cyraulus v e r m i c u l a r i s .  Small, numbers of t h i s species were  c o l l e c t e d and examined from each area.  No trematode i n f e c t i o n was  discovered i n t h i s species.  Comparison with Infection found at San Juan Island ( M i l l e r 1925 ) .  - Tables IV and V indicate that Burnaby Lake s n a i l s are more heavily parasitized than those of San Juan Island, as reported by M i l l e r ( 1925 ) . These tables show i n p a r t i c u l a r that the percentage of i n f e c t i o n and the number of i n f e c t i n g l a r v a l species are higher i n Burnaby Lake s n a i l s than i n those collected on San Juan Island. The species of s n a i l common to both areas ift L . proxima  105. and i n these the difference  i n the degree of i n f e c t i o n of the s n a i l s  of both areas i s p a r t i c u l a r l y evident.  L . proxima from Burnaby Lake  are 24$ infected, by a t o t a l of s i x d i f f e r e n t larvae as compared with L . proxima from San Juan Island which are only 8$ infected, by two d i f f e r e n t i n f e c t i n g species. ...The Physa spp from Burnaby Lake also show a higher degree of i n f e c t i o n than the Physas reported by M i l l e r .  Burnaby-Lake ,  Physae were 73$ infected, while only 3$ of the San Juan Island physa were i n f e c t e d .  In the s n a i l s of both areas much v a r i a t i o n i n i n f e c t i o n of i n d i v i d u a l species was found.  There appears to be no r e l a t i o n be-  tween the degree of i n f e c t i o n of a s n a i l species in-one area with the same species i n the other.  The degree of i n f e c t i o n i n the snails  seems to be a c h a r a c t e r i s t i c of the l o c a l e .  Summary of Host Records for Burnaby Lake L a r v a l  Trematodes.  The following i s a l i s t of s n a i l s found at Burnaby Lake which were found shedding each c e r c a r i a / . plete host records f o r each cercarvfae  E »C » 1 . . . . . . . Pseudosuccinea columella Lymnaea proima L. palustris Physa occidentalis  Tafcle V I gives the com-  106. P. c f . t r a s k i i Helisoma t r i v o l v i s  E . G.  2. Pseudosuccinea columella P. occidentalis H. t r i v o l v i s  X.C. 1 L . proxima L. palustris H'. t r i v o l v i s X.C.  2 H. t r i v o l v i s  F .C. 1  j  >  Pseudosuccinea columella L . proxima L. palustris P. occidentalis P. t r a s k i i H. t r i v o l v i s  F.C.  2  :  Pseudosuccinea columella L . proxima P. occidentalis  ::  •  > _  107.  Evidence of Host S p e c i f i c i t y of Cercariae.  There appears to be l i t t l e s p e c i f i c i t y showk by trematode m i r a c i d i a i n f e s t i n g Burnaby Lake i n the choice of s n a i l hosts.  The greatest degree of host s p e c i f i c i t y has been found with X.C. 2, which was found in-one snail- species only, that-of H. trivolvis.  X.C. 2 and F .C. 1 show the next highest degree of host  s p e c i f i c i t y , f o r each are found i n three species of s n a i l only, which f a l l into two separate genera.  E .C. 2 was found i n -three species of  s n a i l s , comprising three genera.  E.C. 1 and F.C. 1 exhibit the l e a s t  amount of s p e c i f i c i t y i n choosing t h e i r intermediary hosts.  Both  cercariae were shed from the same host species, comprising s i x species of three different genera.  It may be -of interest to add here that H.M'. M i l l e r J r . ( 1925 ) observed that no one of the nine species of furcocercous cercariae he found at San Juan Island were shed from more than, one genus of s n a i l host.  Cort ( 1915 ) found furcocercous forms para-  s i t i z i n g three generalof s n a i l s i n Michigan. Evidence of Multiple i n f e c t i o n ofSnail  Hosts:  No case of a s n a i l playing host to more than one species of l a r v a l trematode was found i n the s n a i l s of Burnaby Lake. A l though t h i s would appear t o indicate the existence of a natural immunity of Burnaby Lake snails to second i n f e c t i o n , the r e l a t i v e l y small number of s n a i l s examined prohibits such a conclusion. The  108,. presence of.two species of rediae or sporocysts within an i n d i v i d u a l s n a i l may have been obscured due t o the small amount of one or the other present and lack of experience i n distinguishing rediae and sporocysts on s p e c i f i c  grounds.  I t can be d e f i n i t e l y said that no s n a i l from Burnaby Lake, from which cercariae emerged, shed more than one type during the time i t was under observation. . -  I n the case of each of the s i x cercariae discovered, the  snails shedding the cercariae were i n severa^instances found to be harbouring echinostome^or metacercariae of another species. s n a i l s were also found t o contain both echinostome  Mary  and large un-  i d e n t i f i e d cysts.  Evidence of Harm done to S n a i l Hosts:. I t i s d i f f i c u l t to determine whether or not l a r v a l teematodes l i v i n g within s n a i l s can be a cause of the s n a i l s ' death. Several s n a i l s wererproved on examination t o be extremely p a r a s i t i z e d , t o the extent that the l i v e r or digestive gland was composed almost exclusively of^sporocysts and rediae.  These s n a i l s i t i s  true, may have died from old age rather than from the cumulative effect of harbouring the active l a r v a l worms. Examination, nonetheless, showed that very l i t t l e of the normal tissue could be found.  Rees ( 1931 ) reports much the same condition i n the case  of the l i v e r fluke, F a s c i o l a hepatica. Here, he reports, the intramolluscan stages create much d i s i n t e g r a t i o n of the s n a i l host,  .109. reducing the l i v e r c e l l s to a t h i n layer of protoplasm containing the. nuclei..  In the.case of infec-cad Burnaby Lake s n a i l s , the digestive gland was i n v a r i a b l y found to have an unhealthy appearance.  Most  cases were such that the infected portion of the s n a i l was l a r g e r i n mass than the uninfected portions.  The infected digestive gland  varied from a cream to rust i n colour.  I t i s apparently the rediae which are agents of most of the destruction within the s n a i l hosts. -Rediae. are muscular and capable of independent movement. In addition, they have a mouth, surrounded by a sucker, and i n some cases may be provided with an anterior c e l l a r of spines. I t i s conceivable, then, that as a r e s u l t of t h e i r movements and feeding these larvae are capable of causing much destruction within s n a i l s . The infected s n a i l , i t must be noted, seems to be able to present some degree of fortitude and counteraction to the presence of l a r v a l trematodes.  Active and apparently healthy s n a i l s have been  examined which contained nothing more than a sac of active cercariae i n place of the digestive gland.  Brown ( 1926 echinostome  ) i s of theoopinion that snails infected by  and xiphidiocercariae die sooner than those infected by  furcocercous forms.  A s i m i l a r observation has been made i n the  case Of Burnaby Lake s n a i l s .  I t was found that those s n a i l s which s  110.- * shed cercariae and l i v e d longest had the furcocercous. cercariae emerging from them.  In summarizing  the harmful effects of l a r v a l  upon t h e i r s n a i l hosts, Brown ( 1926  trematodes  ) makes the statement,regarding  Echinostome cercariae, that " i t i s very d i f f i c u l t t o estimate the e f f e c t s of these parasites, i n t h e i r hosts, that they, are harmful, i s indisputable," which i n general covers the s i t u a t i o n found with a l l cercariae species at Burnaby Lake.  I n f e s t a t i o n by metacercariae appears to. have no detrimental effect upon the s n a i l .  This i s to be expected since metacercariae  are non-motile and non-feeding.  Large clusters or " clumps" of  cysts were often found in. s n a i l s , but.apparently t h e i r presence i n quantity Is as innocuous as single i n f e s t a t i o n s .  111.  SUMMARY  Six species of l a r v a l trematoda have been discovered i n the Mbllusca of Burnaby Lake, B.C.  These cercariae emerged from s n a i l s  collected over a period of one year.  A l l snails examined came from three s p e c i f i c areas of Burnaby Lake.  They were observed i n aquaria f o r the natural emergence  of cercariae, or crushed to detect the presence of other i n t r a molluscan stages.  The, nature and intensity., of the l a r v a l trematode  i n f e c t i o n has been noted and the d e t a i l s for each presented i n t a b l e s .  The cercariae found comprise two species each of echinostome cercariae, furcocercous cercariae and x i p h i d i o c e r c a r i a e .  The  tentative i d e n t i f i c a t i o n s of E.C. 1 and E .C. 2 f o r the echinostomes, F.C. 1 and F.C. 2 f o r the f o r k - t a i l e d and X.C. 1 and X.C  2 f o r the  xiphidiocercariae were made. Comparisons and tentative i d e n t i f i c a t ions with cercariae reported i n the l i t e r a t u r e have been carried out. The r e s u l t / of these comparisons i s as follows:  E.C. 1  Cercaria echinoparyphium recurvatum ( proved by i n f e c t i o n experiment }.  E . C. 2  C. echinostomum revolutum ( indicated by close morphological resemblances ) .  F. C. 1  „  shows resemblance t o C. dohema, Cort and Brackett 1937.  112  F.C. 2  shows resemblance t o C . oregonensis »• Macfarlane  and Macy, 1946 ; and C. m i l l e r i ,  Faust 1926 . X.C. 1  shows much resemblance t o C. a l b u i , Brooks 1947..  X.C. 2  appears to be an undescribed species.  Each species of l a r v a l trematode has been described. A series of extensive observations and experiments were conducted t o discover the possible l i f e cycle of each of these l a r v a l worms.  These l i f e cycle studies have included l ) a survey of the  naturally infected s n a i l s , as well as some tadpoles and c a t f i s h , to determine which species act as intermediate hosts t o l a r v a l trematodes, 2)-exposure of laboratory-raised s n a i l s , and of Burnaby Lake tadpoles and c a t f i s h , t o attack by various cercariae, and 3) feeding of the-encysted  cercariae to various vertebrates i n order to discover  which are the adult hosts of the trematodes.  The l i f e cycle of E.C. 1 ( a at Burnaby Lake has been demonstrated.  6chinoparyphium recurvation ) The f i r s t intermediate host  of t h i s worm has been determined as being Pseudosuccinea columella, Lymnaea proxima, L . p a l u s t r i s , Physa occidentalism P. c f t r a s k j i and Helisoma t r i v o l v i s .  E.C. 1 u t i l i z e s the same s n a i l species f o r  both the f i r s t and second intermediate hosts, f o r metacercariae have been found i n the Wolluscan species from which cercariae emerged.  Three species of laboratory-raised s n a i l s have been  ;.-  .113.  infected by E.C. 1. These experimental second intermediate hosts are B'seudosuccinea columella. P. occidentalis and P. cf t r a s k i i . Metacercariae identical with the 45-spined experimentally produced cysts of E.C. 1 were fed to guinea pigs, rats, ducklings and pigeons.  In one-pigeon, eight small.adult echinostomes were dis-  covered 33 days after the experimental feeding. These worms have been identified as Echinoparyphium recurvatum.  Close morphological  comparisons of E.C. 1 and i t s cyst with the adult trematode, and the fact.that, as far as could be determined, the pigeon was free of trematode infection prior to the experiment, indicates that E .0. 1 i s the larval stage of Echinoparyphium  recurvatum.  Several unsuccessful experiments were made to determine possible intermediate hosts of F.C. 1. Thisc'cercariae has been identified as a^haryngeal longifurcate distome cercariae, and i s very likely.the larval stage of a strigeid trematode.  I t was proved  to be incapable of producing schistosome dermatitis i n humans. The second furcocercous cercariae found at Burnaby Lake has been discovered capable of producing dermatitis or " swimmer's itch •' i n humans. The symptoms recorded agree generally with those reported i n the literature for other schistosome dermatitis experiments. Although the two xiphidiocercariae were very similar morphologically, they have been classed as separate species on the basis of stylet structure.  The f i r s t intermediate hosts of X.C. 1  :  .  _  .  114. .  are !••« proxima* L . p a l u s t r i s and H. t r i v o l v i s . .No n a t u r a l l y i n fected second intermediate hosts of t h i s cercadae were discovered. A gammarus species was proved t o be at l e a s t an experimental second intermediate host.  X .C. 1 was unable to be infected i n ducklings,  g o l d f i s h , r a t s and guinea p i g s .  X.C. trivolvis.  2 was  found i n only one s n a i l species, thatoof H.-  A gammarus species was found to be an experimental  inter-  mediate host of t h i s cercariae^.  B urnaby Lake was found to have a high degree of l a r v a l trematode i n f e c t i o n , both i n the number of species of larvae and i n the number of s n a i l s i n f e c t e d .  There i s at least an apparent d i f f e r e n c e . i n s n a i l populations, and. t h e i r l a r v a l trematode fauna, between s n a i l s of the-three areas under study at B urnaby Lake.  The Deer Creek area has the  r i c h e s t oSblluscan fauna, and i t s snails have the highest incidence of i n f e c t i o n by l a r v a l trematodes.  There appears to-be l i t t l e or no host s p e c i f i c i t y i n the l a r v a l trematodes at Burnaby Lake.  X.C. 2 exhibits the only n o t i c -  eable degree of s p e c i f i c i t y , being found i n H. t r i v & L v i s only. A l l theootherocercariae are found i n s n a i l species comprising at l e a s t two genera. F.C. 2 has been proved a causative agent of dermatitis.  schistosome  As f a r as can be determined, t h i s i s the f i r s t experi-  115. mental demonstration of sctaistosome dermatitis i n B r i t i s h Columbia. The dermatitis i s manifest by the production of erythematous papules and i t c h i n g .  EXPLANATION OF LETTERING- OF PLATES.  act, anterior c o l l e c t i n g tubules,  mt, main excretory tubule,  bp, b i r t h pore.  l p s , lappet spine region,  c, caecum.  n, "notches " or " crenations ".  cb, caudal bodies or blocks  o,  cer,  ob, oral bulbous or s u c t o r i a l  cercaria.  ovary.  eg, cephalic or penetration gland.  oe, oesophagus  cgd, cephalic gland duct,  og, o r a l gland.  c l , collar.  os, o r a l sucker.  cs, c u t i c u l a r spines or h a i r s .  ow,  cw, cyst w a l l .  p, pharynx.  ds, dorsal spine region.  pig, pigment.  ext, excretory c o l l e c t i n g tubule.  pph, prepharynx.  ep, excretory p a p i l l a .  s, s t y l e t .  es, eyespot.  sd, shoulder region.  ev, excretory v e s i c l e .  sp, s u c t o r i a l proboscis.  f c , flame c e l l .  [ss, sucker spines.  f f , f i n f o l d or membrane.  t, testis.  f r , f u r c a l ramus.  t s , t a i l stem.  g, gut  u, uterus.  gs, spines of glands,  v, v i t e l l a r i a *  i c , immature c e r c a r i a .  vent, v e n t r a l surface.  Is, l a t e r a l spine region.  vtd, v i t e l i n e duct.  outer cyst w a l l .  apparatus.  Stenaxy of -^eewrreias© offl€«arlaefeyl o s t and Area. Mm  .  AHHU  KB « I1 «S».  Mo. !?» snail® inf®ete&' ©it!* Ifo.tte. s n a i l s iafeeted wits* ©©re*.'. sp. $sd. • ' sp. 801 sag 381 m f08 urn &ss mi iD3a mi 1  in proadttts.  s  paluatris  i  r  occidentalis P. trasMl ftellesnsa trivolvis  45  45  1  1  ; i '.  31  4  a  89 1 (  i  I  .  I  10 •  , i  1  1 JBfiS P01  1  74 28  enailfc tef eoted witl* % i a l  Hxd. -  2 ' i  45  2  2  19  2  2  0  259 -i  34  i -  ' ' 4  1  1  2 4  I  1  Is  140. &7  8  12  •  co©|j©ri %raul«a v«i«ieislaris  0  0  2  s  ;  so  v  ;  $  ;  27  4  «  5  Iter^issia 0 2  g®  $  a  d  160 '11  2 7  I  11  g  So. Snails  Exd.  SS2  TABLE II. Summary of Occurrence of Encysted Forms by Host and Area. LAUT PARK AREA. SNAIL SPECISS. Pseudosuccinea columella Lymnaea proxima L. palustris  DEER GREEK AREA.  STILL Gmm AREA.  Wo. No. snails infected with No. No. snails infected wit* No. No. snails infected withtotal Exd. cysts. Sxd. cysts. cysts. Exd. Exd. Echinost. Unident. Sohinost cysts Unldent. ichlnost. Unideht. cysts cysts cysts oysts. cysts 170  36  9  43  3  1  1  1  1  Physa occidentalis 66  14  >  0 8  2  39  5  22  3  18  3  2  19  1  252 26  19  6  4  36  20  7  121  8  5  2 ,  14  10  4  48  1  2  2  1  anceps  0  0  Menetus cooperi  2  5  Gyraulus verraicularis  4  1  0  3'  Ferrissia caurina  0  0  0  0  P. traskii Helisoma trivolvis H.  TOTALS.  26  273  , 41 10  88  18  79  2  29  1  4  3  3  19  9  152  5  36  26  14  504  Percent o f a l l S n a i l s examined i n f e c t e d with liatramblluscan stages o f Larval l^eraatodes.  ARM mm fHica SIMLS  LfiBVAL STAGES AH© EESSS4T •BSHBCT.JOT- M  ' mas QOE&mm  Eehinostome cercariae  taut Park  S t i l l Greek Beer Greek  U.B.  Siphielio- gurcoeercotts Gfereariae cercariae • eei^oarlea and other Cysts Intramolluscan 0.7$ 1% "•  8$  i 2.0$  &&-Stf£XSiS SKA&BOED.  1.6$  2.2^  ^ Based on this examination <§f §04 specimens ( See Table I I ).  *  TABLE  m  Summary of Larval Trematode Infection i n Burnaby lake Snails. SNAIL* • • SPECIES.  No. Examined  Pseudosuccinea columella Lymnaea proxima palustris Ifnysa r occidentalis Physa cf. traskii ...Meiisoma trivolvis Helisoma anceps Uyraulus vermicularis Perrissia caurina Menetus  cooperi  No. of i n So. - infect% fecting e 3d by cer- infected cercariae cariae spp sp  fo  Probable infected; by No. of total infectTotal i n - ing species. fecting s TO  259  4  5  2%  7  27%  55  4  9  21%  6  24%  24  5  5  15^  5  140  4  57  4  9  iefo  6  70%  12  3  9  7S%  '5  92%  3  0  0  0  0  5  0  0  0  0  0  0  0  0  0  27  0  0  1  26  •  •  12%  Wo  73%  TABLE V. Summary of Larval Trematode Infection i n Snails of San Juan Islands Puget Sound, as given by Miller ( 1925 ). No. SMIL Percent Probable Number of SPEOISS-. Examined Infected Infecting Species  L. proxima  76  8%  2  L. stagnalis  84  65%  6  P. species  75  $%  1  Planorfcis ( 5 or more ) Succinea retusa Sphaerium  376  44$  12  77  0%  0  32  <y% "  0  * Summary o f Life Cycle Studies Natural and experimental hosts o f l a r v a l trematodes found a t Burnaby lakes  •ass®.  ' flK9 '  ( a i l m&tfoXlsr iafsetea) .3^©rfiaeatall^r feetedU  feoted.  FBSuStoisaiGcinea  eoliBsellsi.  l&lisscsa trivi&vis  • !*> f^asiEa-' I* f a l t i s t r i s P. 'aeei^i.talis J*. o f t r a s & i i %  trfvdivis  rBO-atiosaccinea W. .oecSdsatslis H. ti^slvi©  SQluiaslla  ©eewfeiitalis  C  Eusfej-t  • .". { wa^ttifal ,). '"  of tr&£fcii'  3£» ©• 1  L. ps&ttstspSs. a. feiv^ivta 1!. trtvplvis.  Bp —  SejBmajFus eg '(. -3% .; •11.,  i-scaooBuecanea  •>J?»-0. 1  <ajl«asa.la L. proadLsja falast^ia P. escM@«,t^.i|SF* ef' t r a s k i i ' • .11. t r i v o l v i s FgessaiiGt saeotasa  eolyraslla  #eei#eatslis  —  m mini  mmm  116. LITERATURE CITED. Baylis, Hi.A. 1929.  Manual of Helminthology, Medioal and Veterinary. London.  Beaver, P.C. 1937.  Esperimental studies on Echinostoma revolutum (Froelich), a fluke from birds and mammals. 111. B i o l . Mbnogr. 15 ( 1 ): 1-06. 3pl.  Brackett, S. 1940.  Studies on Schistosome dermatitis. V. Prevalence i n Wisconsin. Amer. J . Hyg. 3__: Sec. D: 49-63.  1941.  Schistosome dermatitis and i t s distribution. , Symp. on Hydro biology. U. Wise. Press: 360-378.  Brooks, F.C. 1943£ a ) . Larval trematodes of Northwest Iowa I . Nine new xiphidiocercariae. J . Parasit. 29_: 330-339; f i g s . ____________  1943 ( b ) . Larval trematodes of Northwest Iowa I I . Four new strigeids. J . Parasit. 29: 340-347; figs.  Brown, F .J.  1926.  Some British fresh water larval trematodes with contributions to their l i f e histories. Parasitol. 18: 21-24; 3 p i . ; 30 f i g .  Cort, W.W.  1914.  Larval trematodes from North American fresh water snails.  J . Parasit. 1:  65-84; 15 f i g s .  117. Cort, W.W. 1915. Some North American larvaltrematodes. 111. B i o l . Monogr. It 447-532 ; 8 p i . 1928. Schistosome dermatitis i n the United States. ( Michigan ). Jour. Amer. Med. Assn. 90: 1027-1029. •  1936 ( a ). Studies on schistosome dermatitis I . Present status Of the subject. Amer. J . Hyg. 23: 349-371. 1936 ( b ) . Studies on schistosome dermatitis IV. Further information on distribution i n Canada and the United States. Amer. J . Hyg. 24: 318-333.  Cort, W.W. and Brackett, S. 1937. Two new species -of strigeid cercariae, from the Douglas Lake region, Michigan. J . Parasit. 23: 265-279. 1938. A ngvp strigeid oercaria which produces a bloat disease of tadpoles.  J . Parasit. 24: 263-271;  1 pi. 1 fig. Cort, W.W. and Talbot, S 3 . 1936.- Studies on schistosome dermatitis.  I I I . Observations on the behavious of  the dermatitis-producing schistosome cercariae. Amer. J . Hyg. 23j 385-397. Dawes, B. 1946. The Trematoda, with special reference to British and other European forms. Camb. Univ. Press 1946.  118.  Harper, W.F. 1929.  On the..structure  and l i f e history o f - B r i t i s h  f r e s h water l a r v a l trematodes.  P a r a s i t o l . 2_1:  189-199; f i g s .  1931.  On the structure and l i f e h i s t o r y of B r i t i s h f r e s h water furcocercariae.  P a r a s i t o l 23:  310-325; f i g s . Hunter, G.W. I I I .  Shillam, D.S., T r o t t , O.T., and Howell, E.V.. J r . 1949.  Shistosome dermatitis,in Seattle, Washing-  ton. J . P a r a s i t . 35: 250-254; p i .  Faust, E.C. 1917. L i f e History studies on Montana trematodes.  111.  B i o l . Monogr. 4 ( 1 ) 1-120; 9 p i . 1 f i g . .  1924.  Note on l a r g a l flukes from China, I I . Amer. J . Hyg. 4: 241-300.  1926.  Further observations on South A f r i c a n l a r v a l trematodes. P a r a s i t o l . 18: 101-128.  Johnston, J . C 1920.  The l i f e cycle of Echinostome revolutum ( F r o e l i c h ) . Univ. C a l i f . Pub. Zool. 3_9 ( 11 ): 335.-388; pis.; f i g s .  Lebour, M.V. 1911.  <  A review of B r i t i s h marine cercariae.  Parasitol.  4 : 416-456 . 2 p i .  Macfarlane, D .G. and Macy,_R .W. 1946.  Cercaria oregonensis, n sp ,  a dermatitis-producing Schistosome cercariae  119. from the Pacific Northwest. J . Parasit. 32: 281-285. MacMullen, D.B..and B eaver, P.O. 1945. Studies on schistosome dermatitis IX. The l i f e cycles of three dermat i t i s -producing schistosomes from birds and a discussion of the subfamily Bilharzielinae ( Trematoda: Schistosomatidae ). Amer. J . Hyg. 42: 128 - 154. Manter, H.W. 1926. Some North American.fish trematodes.  111. B i o l .  Mbnogr. 10: 127-264; 6 p i . , 1 f i g . McLeod, J.A. 1934. N"otes on cercarial dermatitis with descriptions of the causative-organisma, flercariae wardlei n spy Cercariae ba.jkovi n sp, and the parthenogenetic stage of Cercariae elvae Miller.  Can.  Jour. Res. 10: 394-403. Miller, E.L. 1936. Studies on North American cercariae. 111. B i o l . Monogr. 14, ( 2 ): 1-125. 8 p i . Miller, H.M. J r . 1925. The larvae trematode infestation of the fresh water Molluscs of San Juan Island, Puget Sound. Wash. Univ. Studies. Ser 13: 9-22. 1926. Comparative studies on Furcocercous cercariae. 111. B i o l . Monog. 10 ( 3 ): 1-103; 8 p i . 2 fig.  • 1927.  120. ,.  Furcocercous larval,'treiaaiodes from San Juan Island, Washington.  Musfeldt, I.W.  ..  1945.  P a r a s i t o l . 19: 61-83.  I.- Parasites of the muskrat ( Ondatra Zibet hie a ) at Burnaby Lake ( Vancouver) B.C. ) I I . Preliminary l i f e history studies on Echinostomum coalitum'Barker a n d C A . Beaver,  .  ;  v  ..  1915. ( Trematoda, Echlnostomidae ) . E .A. Thesis. Univ.. of B.C.  '  .  1947.  The significance of diseases and parasitism of the muskrat ( Ondatra zibath&ca ) i n B r i t i s h Columbia. M.A.  O l i v i e r , L . 1947.  Thesis. Univ. of B.C.  Observations on experimental dermatitis i n humans. induced by cercariae of T r i c h o b i l h a r z i a stagnicola ( Talbot, 1936 ) .  Porter, A. 1928.  J . P a r a s i t . 3_3 ( Suppl.) 9-10  The larval/trematoda found i n c e r t a i n South A f r i c a n mollusca, with s p e c i a l reference to schistosomiasis (-Bilharzias ) .  S. A f r . I n s t . Med. Res. 8_ ( 42 ):  492. 83 p i . 1 f i g .  Rankin, J.S. J r . 1939.  E c o l o g i c a l studies on l a r v a l trematodes from Western-Massachusetts. J . P a r a s i t . 25: 309328? 3 p i .  Rees, (l. 1931.  Some observations and experiments on the biology of l a r v a l trematodes. P a r a s i t o l 23: 428-440.  121. Stankard, H.W. 1929. The excretory system of Cryptocotyle ( Heterophyidae ). J . Parasit. 15: 259-266.  ;  1946. Possible snail hosts of human schistosomiasis in the United States. J.'Parasit. 32: 539-552.  Swales, WJ3. 1935. The l i f e cycle of Fasciolo ides magna ( Bassi, 1875 ), the large liver fluke of ruminants i n Canada. V/ith observations on the bionomics of the r  larval stages and tte intermediate hosts, pathology of F. magna and control measures. Can. Jour. Res. __2: 177-215.  1936. Schistosome dermatitis i n Canada. Notes on two causative agents and their snail hosts i n Manitoba. Can. Jour. Res. 14 ( 1 ): Sec. D. Talbot, S .B . 1936. Studies on schistosome dermatitis. I I . Morphological and l i f e history studies on three dermatitis producing schistosome cercariae, C. elvae Miller, 1923, C. stagnicola n sp and. C physella n sp . Amer. J". Hyg. 23: 372-384. 1 pi.  1  

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