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UBC Theses and Dissertations

An investigation of the inter-relationship of growth and regeneration Parizeau, Paul Henri Delpe 1943

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AKF INVESTIGATION OF THE EWER-RELATIONSHIP OF- GROWTH AND REGENERATION by Paul H. Di Parizeau A Thesis submitted in Partial Fulfilment of The Requirements for the Degree of M A S T E R O F A R T S in the Department of ZOOLOGY The University of British Columbia APRIL, 1943 Contents. INTRODUCTION .. ...... ACKNOWLEDGEMENTS. MATERIALS AND METHODS.. PART I . Euplanaria dorotocephala (Woodworfch)-.-Experiment I».......................... Experiment. I I Experiment I I I . . . . . . . . . . . . . . . . . . . . . . . . . Experiment IV. Experiment V..... Experiment VI.......................... PART I I . Hyla r e g i l l a B a i r d and G i r a r d . ....... RESUXJTS/* »••«••####••••••••••••••*••••••*•«••••*•••••• PAR.T X• • • • • • ##••••#•*••••••••••••••••••••••••• Experiment I,....#..».•*•••«••••••••*•. Experiment I I * . . •*•««»•*•*• • .• • • Experimenb III«• •»••«•••••••«•••••«•••• Experiment IV. Experiment \/"«.......................... Experiment VI.. PART I I . . . . . . . . . .......................... DISCUSSION... PART I . . . ... PART I I . .... Contents (Cont'd.) CONCLUSIONS•••••••••••••••••••••••••••••••••••••••••••• LIST OF H i i j ^ S R S N C E S • • • • • • • • • • • e o « « « « » * « » e « * « e ^ « « « * « * « o * * L i s t of I l l u s t r a t i o n s . P l a t e I . Figure 1. S p e c i a l s c a l p e l f o r d e c a p i t a t i n g p l a n a r i a n s , i n - . Part I 5 experiment I I . Figure 2. P l a n a r i a n d e c a p i t a t i o n l e v e l used i n Part I , experiment I I . P l a t e I I , General plan of Part I, experiments IV. V and VI. P l a t e I I I . Figure 3. Level of tadpole t a i l amputation used i n Part I I . Figure 4. Conception of tadpole body length used i n Part I I . Figure 5« Hind l i m b developmental stages 1, 2 and 3 of tadpole used i n Part I I . P l a t e IV.. Figure 6. Closed-in pool used i n Part I I . ( l i d i n p l a c e ) . Figure 7» Glosed-in pool used i n Part I I . ( l i d removed). P l a t e V. Graph of percentage change i n length as recorded i n Part I , experiment I I . (Table 7') • 1. ACKNOWLEDGEMENTS Dr. ¥. A. Clemens, who d i r e c t e d the work, went out of h i s way to render assistance whenever i t was required,, I am deeply g r a t e f u l . I am als o g r e a t l y indebted t o Dr. V. C. Brink f o r working out the s t a t i s t i c a l treatment of the data. My f a t h e r and mother were, as always, a great help. I t i s indeed a pleasure t o acknowledge t h e i r a s s i s t a n c e . To a l l those who have a s s i s t e d i n c o l l e c t i n g and caring f o r specimens employed i n the experiments, I vriLsh to express my apprec-i a t i o n . P a r t i c u l a r l y , I should l i k e to thank Mr. Anthony Embleton who expended a great deal of time and e f f o r t t o help i n many of the experimental and t h e o r e t i c a l phases of t h i s undertaking. To Miss Hazel Hawkins I should l i k e t o express my thanks f o r her e x c e l l e n t work i n t y p i n g the copy. z. INTRODUCTION A d e f i n i t i o n of regeneration has been suggested by Y/eiss (s39)« "Regeneration i s the r e p a i r by growth and d i f f e r e n t i a t i o n of damage suffe r e d by an organism past the phase of p r i m o r d i a l development. The extent of regenerative capacity i s l i m i t e d by ' the extent to which formative c a p a c i t i e s survive the ontogenetic phase". Obviously, t h i s d e f i n i t i o n a p p l i e s equally as w e l l t o r e -generation of an organ as i t does t o regeneration of a group of organs. But these are only two of the three great d i v i s i o n s of b i o l o g i c a l r e p a i r . Weiss goes on t o mention the t h i r d , namely, t i s s u e r e p a i r , and t o d i s t i n g u i s h between i t and organ regeneration, "Regeneration of an organ i s on a d i f f e r e n t l e v e l from mere r e s t i t u -t i o n of an i n j u r e d t i s s u e . The former requires not only the cap-a c i t y to grow but i n a d d i t i o n the presence of f a c t o r s v<rhich w i l l . lead the growing mass i n t o proper d i f f e r e n t i a t i o n and o r g a n i z a t i o n " . Various conditions e x i s t w i t h which compliance must be made > i n order that an organ or an assemblage of organs may regenerate. Weiss p i c t u r e s the c h i e f r e q u i s i t e s i n organ regeneration. "In order that an organ may regenerate the f o l l o w i n g conditions among others must be f u l f i l l e d . There must be a stimulus t o provoke renewed formative a c t i v i t y . There must be c e l l u l a r m a t e r i a l w i t h a s u f f i c -i e n t store of potencies t o produce a l l the h i s t o l o g i c a l d i f f e r e n -t i a t i o n s necessary. There must again be organizing f a c t o r s t o make the r i g h t d i f f e r e n t i a t i o n s appear i n the r i g h t places, t o cause the proper alignments, movements, and f u n c t i o n a l transform-ations of the c e l l s , t o d i r e c t the growth of the r e c o n s t i t u t e d parts i n t o the proper proportions, and t o c o n t r o l the resumption of f u n c t i o n a l a c t i v i t y i n j o i n t co-operation w i t h the o l d p a r t s . F i n a l l y , there must be an adequate supply of food and other v i t a l n e c e s s i t i e s " . V/eiss notes that "these p r e r e q u i s i t e s are e s s e n t i a l l y of the same order as those encountered i n the study of ontogeny". It was at one time thought that the regeneration of an organ c o n s i s t i n g of several t i s s u e s came about when each of the components contributed i t s kind t o replace the missing p a r t . Experiments per-formed t o t e s t t h i s " p r e f o r m a t i o n i s t " notion of regeneration pointed i n s t e a d t o epigenesis as p r o v i d i n g a s u i t a b l e explanation of the o r i g i n of regenerative m a t e r i a l . In t h i s connection studies of regeneration have shown the occurrence of two phenomena,regeneration blastemas and r e s i d u a l l o c a l f i e l d s . The former are known to be common to regeneration i n a l l animals, while the l a t t e r have been worked out i n s e v e r a l vertebrates only. The e a r l y regeneration blasrtema c o n s i s t s l a r g e l y of u n d i f f e r -e n t i a t e d e q u i p o t e n t i a l c e l l s . Later the blastema changes i n t o a "determined" c o n d i t i o n i n which i t s d i f f e r e n t parts have acquired the capacity of s e l f - d i f f e r e n t i a t i o n . The r e s i d u a l l o c a l f i e l d s are responsible f o r the q u a l i t a t i v e determination of the process of regeneration. Each of these f i e l d s extends over a l i m i t e d d i s t r i c t i n the animal. Beyond the l i m i t s of each of the'g regeneration of the p a r t i c u l a r organ f o r which i t i s s p e c i f i c w i l l not occur. A f i e l d d i s t r i c t may be e x t i r p a t e d completely and w i l l be replaced only by the formation of a scar,. Further regeneration i n that area i s then impossible. C h i l d and others have formulated the concept of p h y s i o l o g i c a l gradients. The gradient theory had i t s o r i g i n mainly i n observa-t i o n s on,regeneration i n many of the lower animals. When one of these forms ? a pla n a r i a n f o r example, was cut t r a n s v e r s e l y i n t o fragments, each piece replaced the missing p o r t i o n and ret a i n e d i t s o r i g i n a l p o l a r i t y . The gradient theory was intended t o ex p l a i n t h i s phenomenon/ but has since found wider a p p l i c a t i o n i n the ex-pl a n a t i o n of many problems of development. I t s authors a l s o have stressed repeatedly i t s importance i n any attempt t o a r r i v e at an understanding of behaviour. A considerable body of l i t e r a t u r e e x i s t s dealing w i t h the e f f e c t s of various p h y s i c a l and chemical agents on the process of regeneration. Much of t h i s work was c a r r i e d out i n order to sub-s t a n t i a t e the gradient theory. Most of the remaining l i t e r a t u r e is concerned with the a c t i o n of several endocrine substances and of radiation"upon the regenerative processes. The various hormones seem to react somewhat d i f f e r e n t l y with' each species t e s t e d and i t would appear impossible t o draw any broad conclusions from the data a v a i l a b l e -at present. The evidence from many X-ray experiments i n d i c a t e s that strong i r r a d i a t i o n i n h i b i t s regeneration. This f i n d -i n g i s i n agreement w i t h the f a c t that . p h y s i o l o g i c a l l y young c e l l s are h i g h l y susceptible to the a c t i o n of X-rays. The l i t e r a t u r e on regeneration covers almost a l l of the c h i e f groups i n the animal kingdom, extending from amoeba t o man. Each group possesses a c e r t a i n degree of regenerative capacity ?/hich 5\ often does not correspond e x a c t l y w i t h the powers of the group immediately preceding or follo ? / i n g i t i n the scale of organization. I t appears that regenerative capacity decreases with an increase i n the complexity of organization i n the organism. This r u l e i s not i n f a l l i b l e , however, since the ctenophores, r o t i f e r s and most of the lower p a r a s i t i c forms i n contrast t o many of t h e i r nearest present-day r e l a t i v e s , are poor regenerators. Moreover, c l o s e l y r e l a t e d genera,for instance c e r t a i n of the t r i c l a d s , a r e known to dis p l a y sharply c o n t r a s t i n g powers of regeneration. The a b i l i t y t o regenerate complete organs ends w i t h the r e p t i l e s and t i s s u e r e s t i t u t i o n appears t o be the only form of b i o l o g i c a l r e p a i r per-s i s t i n g as f a r as the mammals. The present work i s concerned p r i m a r i l y w i t h the f o l l o w i n g . problem, Ihen growth and regeneration are t a k i n g place concurrently i n an animal, does each of these a c t i v i t i e s , by means of the under-l y i n g processes involved' i n i t s executions exert an e f f e c t upon the rate at which the other would proceed under the e x i s t i n g set of environmental conditions? S t . H i l l i e r ('28) studied the e f f e c t of i n a n i t i o n on growth of the e n t i r e animal and rate of t a i l regener-a t i o n i n the l a r v a of Amblyst oma.. mexioanum. Blacher and co-workers ('32) found that amputation of the hind l e g at the proper time ac-celerated the regeneration of the t a i l , i n four species of f r o g t a d -poles. This they concluded was because the amputation of any part a f f e c t s the whole animal and thus i n d i r e c t l y affects any other regen-e r a t i n g p a r t , Morosow ('35) discovered that a diet of p u l v e r i z e d human embryo t i s s u e caused an increase i n the speed of metamorphosis and regeneration i n tadpoles of Bufp. bufo-and Rana,,e,sculent,a. From these and other s i m i l a r works i t seemed that some kind of mutual s t i m u l a t i o n occurred i n the o l d and new t i s s u e s of a regenerating organism. This form of give and take showed signs of being c l o s e l y bound up with the, metabolism i n the a d j o i n i n g p h y s i o l o g i c a l l y young and old c e l l s . Since Hyman, C h i l d and others had performed numerous experiments on planarian metabolism, and since these animals were r e a d i l y a v a i l a b l e and made f i r s t c l a s s experimental m a t e r i a l , i t was decided to use Euplanaria doretocephala i n the main s e r i e s of e x p e r i -ments. The employment of some kind of growth-promoting diet appeared as the most p r a c t i c a l nefchod of causing an a c c e l e r a t i o n i n the growth rate of the experimental p l a n a r i a n s . This was done i n order that a comparison of the regeneration r a t e s i n the experimentals and i n the slower growing c o n t r o l s might be made, A die t of earthworm (growth-promoting) and a die t of lean beef (causing l i t t l e or no growth) were used i n the experimental and c o n t r o l groups r e s p e c t i v e l y , Hyla r e g i l l a was employed i n an experiment designed t o supple-ment a section of the p l a n a r i a n work dealing'with the e f f e c t of r e -generation on rate of growth. MATERIALS AND METHODS, PART I . Euplanaria dorotocephala (Woodworth) was employed as the subject f o r a s e r i e s of experiments. The p a r t i c u l a r s of pro-cedure common t o these experiments have been included i n the f o l l o w i n g d i s c u s s i o n . Subsequently each of the experiments has been o u t l i n e d separately. A l l . of the shipments of E. dorotoce-phala were purchased from the General B i o l o g i c a l Supply House, Inc., Chicago, I l l i n o i s . The p l a n a r i a n stock was kept i n a t h i n glass stender, 8-g-" i n diameter and 3" high, shielded from d i r e c t l i g h t , and subject to a m i l d l y f l u c t u a t i n g room temperature. The animals were starved u n t i l s e l e c t e d f o r use i n one of the experiments. Ident-i c a l stenders, i n diameter and 2g-" h i g h s containing 2" of water, were employed i n the experimental work. Handling was done by means of an eye-dropper, care being exercised t o keep t h i s instrument free from mucus accumulation. Throughout the experiments the p^lanarians were kept i n water from the U n i v e r s i t y of B r i t i s h Columbia B o t a n i c a l Garden l i l y pond. This u n f i l t e r e d water was stored i n an amber glass b o t t l e f o r periods g e n e r a l l y not exceeding one week. Tapwater k i l l e d the p l a n a r i a n s . The containers used i n the experiments were covered by g l a s s l i d s , shielded from d i r e c t l i g h t by a c l o t h , and subject g e n e r a l l y t o a temperature ranging from 16° t o 21° C. The water was changed a f t e r each feeding, and unless otherwise 8. s p e c i f i e d the stenders were thoroughly cleaned. Gases of f i s s i o n were recorded as t o the s i z e and number of t h e . p o s t e r i o r zooids as soon as they were observed. A method of random sampling was devised. A p e t r i d i s h about l-g-" i n diameter and \" high was placed i n the stock stender. The water was a g i t a t e d by means of an eye-dropper. The planar-ians that landed on the p e t r i dish were removed to the experiment stender, and the procedure -was repeated u n t i l no f u r t h e r animals were required. Fresh earthworm, ( u n i d e n t i f i e d as yet) and r e f r i g e r a t e d beef were used as food throughout the experiments. The earthworms were maintained i n a quantity of humus and decaying plant m a t e r i a l placed i n a covered c l e a r - g l a s s j a r . The earthworm was prepared as food f o r the planarians by chopping i t t r a n s v e r s e l y throughout i t s e n t i r e length. This was t o prevent any v i o l e n t w r i g g l i n g which might have i n t e r f e r e d w i t h the feeding p l a n a r i a n s . The lean beef, which had been i n c o l d storage p r i o r to i t s use i n the experiments, was purchased as r e q u i r e d , at the S t e r l i n g Food Markets L t d . Store No. 15. A feeding period g e n e r a l l y l a s t e d as long as four hours and i n a l l cases an excess of food was p r o v i d -ed. Various procedures f o r measuring the amount of growth i n planarians have been devised by workers i n t h i s f i e l d . These t e c h -niques have been ap p l i e d t o groups of p l a n a r i a n s , and take i n t o consideration weight, volume, or o v e r a l l length. Length measure-ment has been employed e x t e n s i v e l y by Wulzen, (Pettibone and Wulzen, '34, and other papers), and has proven s u i t a b l e i n the present PLATS I . Figure 1. S p e c i a l s c a l p e l f o r decapitating planarians used i n Part I , experiment I I . This s c a l p e l i s held at the angle shown. Figure 2 . Planarian decapitation l e v e l used i n Part I,' experiment I I . PLATE I f i g . l f i g . 2 work. A l i g h t on one side of the stender caused the animals t o g l i d e smoothly away from the source of i l l u m i n a t i o n . The over-a l l extended length of each organism was then measured by means of a set of geometry d i v i d e r s and a m i l l i m e t e r r u l e . A s p e c i a l s c a l p e l was used t o decapitate the planarians. A s i n g l e clean cut at r i g h t angles t o the antero-posterior a x i s was employed whenever p o s s i b l e . The heads were removed from the stend-er immediately f o l l o w i n g the operation. Healing took place i n a matter of minutes, but probably r e s u l t e d i n some l o s s of length i n the operated animal owing to the c l o s i n g over of the outer margins of the cut surface. EXPERIMENT I . On October 9th, 1942, l60 planarians were d i v i d e d at random i n t o two equal groups. One l o t was fed beef, the other was fed from an earthworm c u l t u r e set up on October 10th, 194-2. Feeding took place on the f o l l o w i n g days;—October 10th, 13th, l6th, 19th, 21st, 23rd, 26th and 28th. A. record was .-obtained of the f i s s i o n occurring i n the two groups. EXPERIMENT I I . On November 6th, 1942, 100 planarians were grouped at random i n t o two l o t s numbering 50 each. Length measurements were obtained i n each case. One group* was fed on beef, the other from October 10th, 1942, earthworm stock. The planarians were fed on the f o l l o w -i n g d a y s : — November 6th, 9.th, 13th, l6th and 18th. Measurements 10. were made on November 14th and 19th«> The earthworm-fed group has been r e f e r r e d t o as the "E" group, the beef-fed animals as the "B" group, decapitated animals the " I I " group, c o n t r o l s the " I " group. On November 19th, the E and B groups each were divided i n t o two l o t s c o n s i s t i n g of 25 planarians apiece. The new groups have been designated as " E j " , " B I " J > " B H " < - 0 n November 20th, between 9*45 and 10s 15 A.M. a l l .-of the B J J animals and, between 10:30 and 10:45 A.M., a l l of the E J J animals were decapitated. In both cases the heads were cut away as near as po s s i b l e t o the p o s t e r i o r margins of the a u r i c l e s (See f i g . 2.) A note was kept of the. f i s s i o n that occurred f o r s e v e r a l days f o l l o w i n g decapita-t i o n In the E j , E J J and B J J p l a n a r i a n s . On November 24th, between 4 s l 0 and 6:45 P.M., the regenerating heads of groups E J J and B J J were examined f o r appearance of the eye spots. Those planarians i n which eye spots were v i s i b l e were measured f o r length e x c l u s i v e of regenerating heads. I t should be noted that a l l length measurements of regenerating planarians were made i n t h i s manner. Those animals i n which eye spots had not appear-ed during the f i r s t s e r i e s of observations were examined once more, from 8:05 t o 9*40 P.M. Observations were c a r r i e d out a l t e r n a t e l y on i n d i v i d u a l s from E J J and B J J . During the course of t h i s proced-ure one of the B J J organisms was l o s t . Also on November 24th, length measurements were made of the E j and Bj animals, and the remaining E J J and B J J organisms. Commencing November 19th and continuing u n t i l December 7th, the planarians i n the four groups were starved. On December "Jth, 11. the E j } E J J , B j and B J J animals were given a s i n g l e feeding from the October 10th earthworm stock. The second period of s t a r v a -t i o n l a s t e d from December fth u n t i l January 5^h, 1943. Length measurements of the f o u r groups were made on the f o l l o w -i n g d a y s ? — November 27th, December 1st, 4th, 1thf n t h 19th and January 5"kk* EXPERIMENT I I I . On January 12th, 1943, two groups, each c o n s i s t i n g of 20 p l a n -arians s e l e c t e d at random from the stock, were measured f o r l e n g t h . One of the groups was fed on beef, while the other was pro-vided, w i t h a d i e t of earthworm from the October 10th stock. The animals were fed during the f o l l o w i n g d a y s : — January 12th5 15th and l8th. Subsequently, they were starved during a period extend-in g from January 18th u n t i l February 2nd„ A d d i t i o n a l length measure-ments were made on January 19th and February 2nd. Cases of f i s s i o n were recorded i n d e t a i l , w i t h s p e c i a l r e f e r -ence t o the extended lengths of the p o s t e r i o r and a n t e r i o r zooids. EXPERIMENT IV. On February 2nd, 1943, the October 10th earthworm-stock used throughout Experiments I , I I and I I I was examined. One h a l f of the 120 earthworms i n the c u l t u r e was allowed t o remain i n the October 10th humusj while the other h a l f was removed t o a quart b o t t l e con-t a i n i n g some f r e s h humus i n which other earthworms had t h r i v e d under n a t u r a l c o n d i t i o n s . The o l d humus stock has been r e f e r r e d 1%. t o as "EX T", the new humus, stock as " E X J J " . On February 9th, three groups of 20 planarians each, were selected at random from the stock, and measured f o r length. One l o t was fed from E X - stock, another from E X J J stock and the t h i r d on beef. Feeding took place on the f o l l o w i n g days:—February 9"kh5 l l t h , 13th and I5th e On the l a t t e r two days f r e s h earthworm from the B o t a n i c a l Garden humus was s u b s t i t u t e d f o r the E X - Q stock. This earthworm stock has been r e f e r r e d t o as the "EZj" stock. Measurements of length were made on February 12th and l6th. EXPERIMENT V. Two of the groups of planarians used i n Experiment IV, namely those fed from EXj and EZj earthworm stock, were employed i n -this experiment. The formerly EXj-fed planarians were allowed t o feed on earthworm from the E X J J stock, those p r e v i o u s l y f e d from the EZj stock now feeding on earthworms (EYj) that had t h r i v e d under n a t u r a l conditions i n the humus used i n the E X j j and E Y J J stocks. The planarians were fed on the f o l l o w i n g days:—February 17th ? l 9 t h , 22nd and 24th. Length measurements were c a r r i e d out i n both groups on February 20th and i n the E X j j - f e d gr 0up on February 25th. EXPERIMENT VI. On February l 6 t h , 1943 » two earthworm stocks were set up. One of them ( E Z J I ) consisted of 6 earthworms taken from the EXj stock and placed i n humus from the B o t a n i c a l Gardens. The other c u l t u r e 13. ( E Y J J ) was made up of 6 earthworms from the EXj stock i n humus from the same source as that employed i n the E X T j stock. Each cul t u r e was maintained i n a c l e a r - g l a s s j a r , 8" i n diameter and con-t a i n i n g about 2" of humus. On February 23rd, 30 planarians were divided at random i n t o two equal groups and measured f o r length. One l o t was fed from E Z J J the other from E Y J J stocky One feeding was given 0 n February 24th. Length measurements were made on February 25th. PLATE I I . General, plan of- Part I , experiments IV, "V and VI. This plan' shows the .various' combinations of humus" and 'earthworms used i n order t o demonstrate -that a ;growth-prdmoting,.sub-stance or'group of substances e x i s t s i n a - p a r t i c u l a r ' t y p e of. humus.. This "plan should be consulted along with "l-Jai ©rials ' and Methods. Part I , experiments IV? V and VI" , and subsequent sections dealing with these experiments. o x ..so £. a. 5 o'sv^ £ x o Q . KJ Li 2)^*2* Li g Q-:^-. oSS^»3Su. LJ x w «• * - Jg " .... X N >~ • O :."-«; Ui Li UJ CD I—I H EH MATERIALS AMD METHODS, PART I I , Egg masses and newly hatched larvae of the P a c i f i c Tree-Toad, Hyla r e g i l l a B a i r d and G i r a r d , were c o l l e c t e d from the large pond near the corner of l6th Avenue and Blanca S t , i n Vancouver on A p r i l l8th, A p r i l 25th and May 1st, 1942. On t h i s " l a t t e r date the survivors from these c o l l e c t i o n s were pooled and removed t o V i c t o r i a , ^ The 95 tadpoles which comprised the stock on May 2nd were di v i d e d at random i n t o two groups, experimental and c o n t r o l , numbering r e s p e c t i v e l y 47 and 48 i n d i v i d u a l s . A small dip-net was used t o carry out the random sampling. The two groups were segregated i n two 3/4 g a l l o n aquaria w i t h an ample supply of green algae food. On May 3rd approximately one-half of the o v e r a l l length of the t a i l was removed from each of the 47 experimental animals ( f i g . 3 ). A sharp s c a l p e l , was employed i n t h i s operation. By t h i s time a period ranging from 2 - 18 days had elapsed since the animals i n the experimental and c o n t r o l groups had emerged from t h e i r egg masses. The newly operated experimentals were returned t o t h e i r aquarium where they were kept f o r observation u n t i l the f o l l o w -i n g day. On May 4th the sxperimentals and co n t r o l s were segregated PLATE I I I . .Figure 3 . Level of -tadpole t a l l , amputation, used. i n . Part I I * Figure A. Conception of .-tadpole body length used i n Part .11. Figure 5* Hind limb developmental stages' lv--2"':and -3 of t a d -pole used i n . Part -IX. '.Stage 1. - No toe's .in hind limb. buds. -.• Stage 2 . - Toes i n hind\limb.;buds."'-. ' • Stage -3.. - Free, hind limbs. S T A G E Z. STAG-E 3. IS". i n two live cages in an outdoor pond, where they remained throughout the greater part of the experiment. The live cages for the experimental and control animals were identical in structure and dimensions. Construction was of soft wood and galvanized f l y screen. Dimensions .were as follows:—length 12", width 10", height 8", giving a volume of about 9^ 0 cubic inches and a capacity of somewhat over three gallons. Each cage was equipped with a snugly f i t t i n g cover. The live cages wSre placed side by side in a small outdoor pond measuring about 4' in diameter and roughly 1-g-' i n depth. The pond was covered by a permanent gauge wire „ (fig.4,7). The cages were situated i n such a way as to be as nearly ident-i c a l as possible i n respect to the volume of wa*Ser enclosed, and exposure to the morning and afternoon sun, as well as to the effects of climatic conditions such as wind and rain* From the commencement of the experiment unt i l i t s conclusion there was a bloom of green algae i n the pond. The live cages be-came covered with algal growth shortly after they were placed i n the pond. These two sources of food material were supplemented from time to time with plentiful amounts of filamentous green alga from a neighbouring stream. The subsequent occurrence of green faeces was construed to indicate that the tadpoles were feeding on the algae. At no time during the entire experiment did feeding appear to cease, excepting perhaps immediately prior to and during the metamorphic climax. Figure 6. Closed-in pool used i n Part II.' ( l i d i n place) Figure 7. c l o s e d - i n pool used i n Part I I . ( l i d removed) The cage over the pool i s covered with. J " -gauge wire screen permitting the entry of considerable l i g h t . . 16. On May 17th, May 24th and June 7th, thirteen, twenty and thirty-four days respectively following the t a i l operation, representative samples of the experimental tadpoles were compar-ed with representative samples of the controls to ascertain the progress of regeneration. Between May 4th and June 14th three control and ten experi-mental animals perished. Thereafter, and un t i l the end of the experimenty not a single casualty occurred in either live cage. On June 14th a l l of the tadpoles in the experimental and control groups were examined. Measurements of the body length ex-clusive of the t a i l (fig. *t-.) were taken by means of geometry div-iders and a millimeter rule. Th© animals were classified accord-ingly into three size groups. Each of these three size groups was examined for appearance of toes in the hind-limb buds (fig.5" ) or for free hind-legs (fig.*"-). On June 28th these observations were repeated. Two instead of three size groups were recognized, Commencing on June 28th and continuing until September 4th, the animals i n the control and experimental groups were examined nightly between 7'00 P.M. and 8*30 P.M. to determine the condition of the front legs. In case one or both front legs had become detached from the skin window (fig»—)-s the tadpole i n question was removed to an aquarium for further observation, and a note was made of the date. Five aquaria were employed to house the tadpoles during the 17. f i n a l phases of metamorphosis. Two of these were identical 2-gallon aquaria, each containing about two inches of water, and a seasoned wooden landing for the young frogs. Each was equipped with a glass cover. The other three were identical clear glass battery jars each containing a handful of clean sand, about 100 cc, of water, and a landing place, and each supplied with a glass l i d . Light and temperature conditions were the same for a l l five aquaria. A high mortality was observ-ed amongst the experimental animals in one of the 2-gallon aquaria. Chemical conditions in the aquarium were shown to be responsible. Each animal was numbered before being placed i n an aquarium. Thus, individual records could be kept once the appearance of front legs was observed. The completion of metamorphosis was arbitrarily said to have occurred when the t a i l stump had receded to a level in a vertical line with the anus, with no black portion remaining (fig*—)-» Upon death or completion of metamorphosis the animal was preserved in 5% formalin with a label stating number, date of preserving, and the group to which the animal belonged, namely control or experimental. 1 8 . RESULTS. PART I . EXPERIMENT I . Table 1 contains a record of f i s s i o n that occurred between October 10th and October 28th, (Table 1) P l a n a r i a n s . ' Earthworm-fed Beef-fed F i s s i o n 17 4 No f i s s i o n 63 76 Totals 80 80 The data were t r e a t e d s t a t i s t i c a l l y by arrangingtiiemin a contingency t a b l e and employing the c h i square t e s t of s i g n i f i c a n c e . The amount of f i s s i o n o ccurring i n the earthworm-fed planarians was shown t o be s i g n i f i c a n t l y greater than i n those fed on beef. EXPERIMENT I I . In order to obtain a correct i n t e r p r e t a t i o n of the length measurement data i n Experiments I I , I I I , IV, V and VI, i t becomes necessary t o take i n t o c o n s i d e r a t i o n the accuracy of the measurements in v o l v e d . The " e r r o r of measurement" was determined from a check l o t of 24 planarians i n which l e n g t h measurements were made at d i f f e r e n t times. The values thus' obtained, which i n theory should be i d e n t i c a l , were 206.5 mm., 204.5 wm. and 200.5 mm. As can be seen, t h i s c o n s t i -t u t e s an appreciable e r r o r i n measurement. This e r r o r of measurement i s not the experimental e r r o r , but we 1H. might w i t h some assurance assume i t t o be so, since i n a l l p r o b a b i l i t y i t i s the c h i e f c o n t r i b u t i n g f a c t o r i n the experimental e r r o r . Some r e p l i c a t i o n of t r i a l s i s necessary t o obtain a f a i r estimate of ex-perimental e r r o r . This could be done by handling one l o t of 24 i n d i -v i d u a l s as two-lots of 12 i n d i v i d u a l s , or three l o t s of 8 i n d i v i d u a l s , e t c The. standard d e v i a t i o n on the three measurements (206.5> 204.5} 200.5 mm.) i s - 3.05. This represents the standard e r r o r of a s i n g l e determination. The standard e r r o r of a d i f f e r e n c e i s - 4.32 when each l o t i s made up of 24 i n d i v i d u a l s . The necessary d i f f e r e n c e ( f o r odds of 1:19) t o e s t a b l i s h s i g n i -f i c a n c e i s 8.42 mm. or approximately 4.14/C of the t o t a l length f o r 24 i n d i v i d u a l s , (minimum s i g n i f i c a n t d i f f e r e n c e ) . For 15 i n d i v i d u a l s 5_ x 4.14/C = 5• 17°i minimum s i g n i f i c a n t d i f f e r e n c e . 4 For 50 i n d i v i d u a l s 5_ x 4.14/o - 2.95/' minimum s i g n i f i c a n t d i f f e r e n c e . ' 7 This estimate of e r r o r of measurement i s based on measurements c a r r i e d out e a r l y i n the work, and i s l i k e l y a conservative one i n -asmuch as technique improved s t e a d i l y as the experiments progressed. Two other l e s s serious sources of e r r o r were encountered occa-s i o n a l l y . One or two of the planarians sometimes died and d i s i n t e -grated during the p e r i o d e l a p s i n g between two sets of measurements. In order t o remedy t h i s s i t u a t i o n , the mean of the second set of measurements was m u l t i p l i e d by the number of missing p l a n a r i a n s , and the r e s u l t i n g f i g u r e was added t o the t o t a l of the second set of measurements. The corrected t o t a l was compared w i t h the t o t a l f o r the preceding set of measurements. However, the co r r e c t i o n s were dropped i n comparing the t o t a l s f o r the second and a t h i r d set of measurements. - During the time that elapsed betv/een two sets of mea-surements, f i s s i o n sometimes occurred i n a few of the animals. The The extended length measurements of the p o s t e r i o r zooids were added to the t o t a l subsequent length measurements of the pla n a r i a n s . The corrected t o t a l thus obtained was t r e a t e d i n the same manner as the corrected t o t a l p r e v i o u s l y described. Table 2 contains a record of the i n f l u e n c e of the pr e l i m i n a r y feedings of earthworm and beef upon the length of the planarians. (Table 2) Date of Date of Group E Group B Group E Group B feeding measuring T o t a l T o t a l % change $ change length i n length i n i n o r i g i n a l i n o r i g i n a l mm.(50 i n - mm. (50 i n - l e n g t h . length, d i v i d u a l s ) .dividuals) +12,3$ +3=6$ +12,3$ -7.5$ Following d e c a p i t a t i o n on November 20th i n the E J J and B J J groups f i s s i o n occurred i n a number of the animals. The data are l i s t e d i n Table 3. . Nov. 6 575.0 537.0 Nov'. 9 ' Nov. 14 646.0 556.5 Nov! it Nov. 19 645.5 496.5 XI. (Table 3) Date % I B l I f i s s i o n f i s s i o n f i s s i o n f i s s i o n Nov. 20 1 0 0 1 Nov. 23 -1 3 0 2 Nov. 24 1 3 0 1 Nov. 27 0 6 0 5 Dec. 1 0 1 0 0 Dec. 4 and 0 0 0 0 onward t o t a l f i s s i o n 3. 13 . 0 9 t o t a l 24 i n d i v i d u a l s 25 25 25 This data were t r e a t e d s t a t i s t i c a l l y by arrangingtRemin conting-ency t a b l e s and employing the c h i square t e s t of s i g n i f i c a n c e . The amount of f i s s i o n i n the decapitated animals was shov/n t o be s i g n i -f i c a n t l y greater than that i n the c o n t r o l s . Tables 4 and 5 contain a record of observations made at 4:10 P.M. and again at 8:05 P.M., November 24th, on the appearance of eye spots i n regenerating heads of groups E J J and B J J . (Table 4) E 'II 'II;,-2? planarians 24 planarians Eye spots No eye spots 16 9 5 4:10 P.M.-6:45 P.M. 19 Eye spots No eye "spots (Table 5) E H B I I . 9 planarians 19 planarians 4 5 3 16 8:05 P.M.-9|40 P.M. (Table 6) Combining Tables 4 and 5* E I I " B l I 25 planarians 24 planarians.. Eye spots 20 8 4:10 P.M. -No eye spots 5 16 9:40 P.M. The data weeetreated s t a t i s t i c a l l y by arrangingtUfemin contingency t a b l e s and applying the c h i square t e s t of s i g n i f i c a n c e . The number of times eye spots appeared i n the S T[ group during the course of the observations was shown t o be s i g n i f i c a n t l y greater than i n the B J J group. Table 7 contains a r e c o r d of length measurements taken to show the i n f l u e n c e of a period of s t a r v a t i o n , a s i n g l e feeding of earthworm, and another period of s t a r v a t i o n upon the length of the planarians i n Groups E j , E J J , B j , B J J . I t should be noted that 1.5 mm. per decap-i t a t e d head f o r a l l planarians' o r i g i n a l l y 9.0 mm or l e s s i n l e n g t h , and 2.0 mm. per decapitated, head f o r a l l planarians o r i g i n a l l y 9.5 mm. or over i n le n g t h has been deducted from the November 19th length measurements i n Groups E J J and Bjl* The f i g u r e s obtained i n t h i s manner should be considered u n r e l i a b l e . They have been included i n Table 7 but have been omitted from-consideration i n drawing conclusions from the main data.. In Table 7 and succeeding t a b l e s the column headed "fc change" contains f i g u r e s representing the percent l o s s or gain i n length from the r e s i d u a l measurement immediately preceding. I n a l l ensuing t a b l e s the term " t o t a l " as a p p l i e d t o length measurements s i g -n i f i e s the le n g t h of a group a f t e r c o r r e c t i o n s f o r f i s s i o n and deceas-ed animals, as p r e v i o u s l y o u t l i n e d , have been added to the a c t u a l mea-Z3. surements. The term " r e s i d u a l " as a p p l i e d t o length measurements should he Interpreted as " t o t a l " length minus co r r e c t i o n s f o r f i s s i and missing animals, or i n other words as observed length measure-ments. The column headed "//•" contains f i g u r e s which represent the number of planarians measured at each date. in CD S3 <D 1-1 •> M &o a © —-9 CD <s5 .3 -a "Vi <D o ^ CD CO P< ccj >> ,© EH a (D <H-*AlA O * . « CM -sh CO W rl CM CM ! *AlA CM CM 4 4 « OO ri t> OCNH CM rH I CM CM * ON : lA O 1A * © * NQ CO CO H CO CM m CM t CM CM •T VA^A O • . « « •=j- vD CO CM rH I CM CM lA*A CM CM VS co CM o i IryO *A . 4 O •=fr •<*• o rH rH CM CM >5-*A m 4 o o o o 0 0. ON CO H C— t~ I CM CM vs. CM I VS. C— » o + 1A1AO ... xO H VA rH rH I CM CM 1A1A CM CM CM « rH ! lA^A O 4 • O rH ON CM rH H CM CM lAO UN, •48 lAW (v-| xO lA H CM CM S 1A*A CM CM H r-l © crj crj «H 4= -P <H O O -H 43 43 t> OS"-* rH CM > > O o lA^A CM CM VS. CO « m 1 000 ... C—CO OS m CM CM CM lAlA CM CM CM 1 OOO 0 o e CO CM xO CM CM v 1A>A CM CM O H a cti © 3 !-. X3 rH © •H 0i «H TO 43 Cj-I © O -H k 4s ^3 CM « ; > o !3 VS. ON o rH 1 OOO ... t— m o o 1 CM CM 1A*A CM CM Xi rH © ri tSj <i4 CO 43 CHI © O -rl k 43 S3 o © PA O Xr\ ... CM rH OO + CM CM «=f-CM CM VS. CM lAlA O 00. ON t— CM CM CM vD boo CM \AlA . . ON CO rH H I CM O pA ^A O 0 4.4 t— 45 t- O fs\ 0 >A IrH O rH 3 CM vs. ! ^A^A CM m H rO © CO fc— C— •§• C— xQ I CM CM CM CM M o HA^A CM CM O 1A » O OOO . . « ON O rH Os O + rH CM lAlA CM CM © •a ® in rH © O -rf 4i tJ O © PA CM ^A &0CM a -•H © ® VS. » CM © O a lA^A » O o o CM CM lA^A O " CM CM © o a © rH © cd «H 4s CH! O -H 43 T3 f^* t— rH rH .44 OOO © © © Q O « CM rH » • « rH CO rO co tr\ CM rH rH I CM CM VS. ^A e O, CM1 i OOO ... HOH Us CM rp rl rl I CM CM rH 00 o « 4 « MD CO CM CM I CM CM CO 5 ... lACO t— OCO rl CM rH I TAlA CM CM © Crf © ^ .  U TJ rH © •H crj «H to -P CH ffl O -ri U 4= "tf ON rH O ffl VS. ON . rH I O lA"^ « « « rH CO CM 1A CM CM H ri I CM CM. CM CM VS. CM rH H t O lAliN, ... SO ONvO m o CM CM CM 8 V5. CO 4 o rH ! O tr\lA 4 A « 'VA CM CM H O rH rH H 8 CM CM CM CM CM CM co rH 1 lAVA O 4 . e loo O CO ICO vO CM rH rH 8 lAlA CM CM © o cd © 3 U rH © H Cj «H CO +3 CH © O -H O CM CO ON rH CM 1A m CM ^A 1A o IsO VA CM H eci •ri to © PLATE V. Graph of percentage change i n le n g t h as'recorded i n Part I, Experiment I I , (Table 7 ) . -Date - date o f measurement. Days elapsing - days elapsing .between two datee of measurement.. % change - fa decrease -or increase i n length of the eh-. t i r e group, as taken from the 'measurement immed-;{ l a t e l y preceding... E J J - earthworm-fed regenerating group. .. E j - earthworm-fed unoperated group. B n - beef-fed regenerating group. Bj - beef-fed unoperated group. This graph should be consulted along with Table/7. Li z c LJ Ui 1 r X <3»v 1 c X z 3 •J9 oo I T oo 6 cr o oo CO I I 6 I UK •:OZ-"fO t 6 I Q o Ujrl" O o o •»--*-K> o + T 6 +• cr T + 00 i i J, d 00 6 i 4-Jo o _ z O cr m •PH EXPERIMENT I I I . Table 8 contains a record of the in f l u e n c e of a diet of EXj earthworm stock and a beef diet upon the length of the planarians, (Table 8) Date of Date of feeding Measuring Group EXj Length i n mm.(20 i n d i v -i duals) Group B Length i n mm,(20 i n d i v -i d u a l s ) Jan. 12 t o t a l 257.0 Jan. 12 Jan. 19 t o t a l 26l,0 Jan, 15 Jan. Indifference +4.0 Jan. 18 Jan, 19 r e s i d u a l 248.5 Feb. 2 t o t a l 202.0 Feb. 2 difference-46 , 5 260.5 255.0 -5*5 218,0 190.5 -27,5 EX. j change change +1 *5/o — 2. 1$ -18.7$ -12, Table 9 contains a record of f i s s i o n that occurred between Jan-uary 14th and February 2nd. (Table 9) F i s s i o n No f i s s i o n EXj-fed 3 17. Beef-fed 13 / 7 Totals 20 20 . The data wee«treated s t a t i s t i c a l l y by arrangingtKtr&in a conting-ency t a b l e and employing the c h i square t e s t of s i g n i f i c a n c e . I t was found that the amount of f i s s i o n i n the B group was s i g n i f i c a n t l y greater than that i n the EXj group. %(>. EXPERIMENT IV. Table 10 contains a record of the in f l u e n c e of EX , EX and I I i EZj earthworm diets., and a beef diet upon length i n three groups of pla n a r i a n s . (Table 10) Date of Date of feeding Measuring Group B Group EX-j- Group EX-J-J B Length i n Length i n Length i n mm.(20 i n - mm.(20 i n - mm,(20 i n - $ EX, EX I I $ d i v i d u a l s ) d i v i d u a l s ) d i v i d u a l s ) change change change Feb. 9 t o t a l 185.5 190.0 Feb. 9 Feb.12 t o t a l 188.5 188.5 Feb.11 Feb.12 d i f f e r e n c e +3.0 -1.5 194,5 182.5 -12.0 2 feedings 2 feedings 2 feedings of B bove) +1.6% -0,78^ -6.1% Feb.12 r e s i d u a l 179.0 Feb.13 Feb,16 t o t a l l8l.O Feb.15 Feb.16 d i f f e r e n c e +2.0 (as a- of EX T(as of EZ T A 1 EX, above 188.5 190.0 +1.5 EZi 182.5 198.5 +16.0 +1.1$ +0.79$ *8.7$ EXPERIMENT V. Table 11 contains a record of the i n f l u e n c e of EYj and E X J J earthworm d i e t s upon length i n two groups of pla n a r i a n s . Date of Date of feeding Measuring (Table 11) Group EYj Length i n mm.(20 i n -d i v i d u a l s ) Group EX^-Length i n mm.(20 i n -d i v i d u a l s ) EY -$ change E X l I $ change Feb. 16 t o t a l 198.5 190.0 Feb.17 Feb. 20 t o t a l 227.0 I89.O Feb.19 Feb. 20 d i f f e r e n c e +28.5 -1-0 +14.3$ -0.54-$ Feb. 20 r e s i d u a l 227.0 I89.O Feb.22 Feb. 25 t o t a l — 218.0 Feb.24 Feb. 25 d i f f e r e n c e — +29.0 — +15.3$ 2.7. EXPERIMENT V I . Table 12 contains a record of the influenc e of E Y J J and E Z J - J -earthworm d i e t s upon length i n two groups of planarians. •(Table 12) Date of ' Date of ^ a °. U 8 X e 0 1 Group BY Group E Z T T E Y T T E Z T T feeding measuring Length i n Length i n 1 1 1 mm.(15 i n - mm. (15 i n - % % d i v i d u a l s ) d i v i d u a l s ) change change Feb. 24 Feb. 23 t o t a l 111,5 Feb. 25 t o t a l 120.5 Feb. 25 d i f f e r e n c e +9.0 114.0 127.5 +13.5 +8.1# +11.8# ZQ. RESULTS. PART I I . Table 13 contains a record of the tadpole s i z e groups on June 14th. ; (Table 13) S i z e 1 Size 2 Si z e 3 T o t a l 7-8 mm. 8-11 mm. 11-15 nan. Controls 0 21 24 45 Experimentals 5 - 14 18 37 The data contained i n Table 13 wejsearranged i n a contingency-t a b l e as f o l l o w s . S i z e S i z e 7-11 ram. 11-15 nm. Controls 21 24 45 Experimentals 19_ 18 37 40 42 82 The chi squa,re t e s t of s i g n i f i c a n c e showed that there was no s i g n i f i c a n t d i f f e r e n c e between the s i z e of the c o n t r o l and experiment-a l animals as a whole. However, by regrouping the data i n t o three, s i z e categories i t was p o s s i b l e t o make apparent a d i s t i n c t i o n between the s i z e of the c o n t r o l and experimental animals as a whole. The f o l l o w i n g contingency t a b l e was found s a t i s f a c t o r y f o r t h i s purpose. S i z e S i z e S i z e 7-8 mm. 8-11 mm. 11-15 mm. Controls 0 21 24 45 Experimentals 5 " 14 18 37 5 35~ ~42~ 82 I t was shown that odds of 9*1 e x i s t i n favour of a r e a l d i f f e r -ence, but t h i s i s not acceptable. This does i n d i c a t e , however, that a s i g n i f i c a n t d i fference i n size.might have been obtained had the mea-surements been made at a somev/hat e a r l i e r date. Table 14- contains a record of the tadpole s i z e groups on June 28th. (Table 14) Size 1 Size 2 T o t a l 9-11 mm. 11-16 mm. Controls 8 37 45 Experimentals 7 30 37 The data waee t r e a t e d s t a t i s t i c a l l y by arrangingtiiemin a conting-ency t a b l e , and employing the c h i square t e s t of s i g n i f i c a n c e . I t was found that the c o n t r o l and experimental animals were not s i g n i f i -c a n t l y d i f f e r e n t i n s i z e at t h i s date. Emmett and A l l e n ('19) have found that the various developmental stages of the hind limbs i n f r o g tadpoles form u s e f u l c r i t e r i a f o r the progress of development in' the organism as a whole. A modified v e r s i o n of t h e i r technique was used i n t h i s experiment. The tadpoles were c l a s s i f i e d according t o whether they possessed hind limb buds without t o e s , hind limb buds with toes, or free hind limbs. Table 15 contains a record of the three categories of developing tadpoles on June 14th. (Table 15) Hind limb Hind limb Free hind T o t a l buds buds with limbs toes Controls 27 Experimentals 26 15 7 3 4 45 37 30-The data were t r e a t e d " s t a t i s t i c a l l y by arrangingtKemin a conting-ency t a b l e and employing the c h i square t e s t of s i g n i f i c a n c e . I t was shown that there was no s i g n i f i c a n t d i f f e r e n c e between the stage of development i n the c o n t r o l s and that i n the experimentals as a whole. Table 16 contains a record of the three categories of developing tadpoles on June 2 8 t h . (Table 16) Hind limb Hind limb Free hind T o t a l buds buds w i t h limbs toes Controls 7 4 34- 45 Experimentals 7 2 28 37 The data wefe t r e a t e d s t a t i s t i c a l l y by arranging'CMjnin a conting-ency t a b l e and employing the c h i square t e s t of s i g n i f i c a n c e . I t was shown that there was no s i g n i f i c a n t d i f f e r e n c e between the stage of development i n the c o n t r o l s and that i n the experimentals as a whole. June 28th was the day before the date upon which the f i r s t appear-ance of free fore limbs i n one 'of the tadpoles took place. Taking June 28th as zero, the number of days required f o r each of the c o n t r o l and experimental tadpoles to obtain f re e fore limbs was recorded. Means of 34.5 days f o r c o n t r o l s and 32.8 days f o r experimentals were obtained. S t a t i s t i c a l treatment of the data w i t h a p p l i c a t i o n of the " t " t e s t of s i g n i f i c a n c e revealed that there was no s i g n i f i c a n t d i fference i n the amount of time required f o r the appearance of free fore limbs i n the two groups. 31. Because of the large number of c a s u a l t i e s occurring i n the ex-perimental group (see M a t e r i a l s and Methods Part I I ) , i t was not poss-i b l e t o make a s a t i s f a c t o r y comparison of the time required i n the experimentals and c o n t r o l s f o r the tadpoles w i t h f r e e fore limbs to change i n t o young f r o g s . 3Z. DISCUSSION. PART I . The data obtained i n experiment I I and contained i n Table 2 i n -dicated that an earthworm di e t produced greater growth i n Euplanaria dorotocephala than a diet of lean beef. Experiment I showed that the amount of f i s s i o n o c c u r r i n g i n the earthworm-fed animals was s i g n i f i -c a n t l y greater than i n those fed on l e a n beef. (See Table 1) I n t h i s connection G-reenberg. and Schmidt ( '36) have found that a di e t of lean beef causes l i t t l e or no growth and r e l a t i v e l y few cases of f i s s i o n i n P l a n a r i a maculata. This p a r a l l e l s the r e s u l t s obtained i n experiments I and I I w i t h E. dorotocephala. I n reference to the growth-promoting power of the earthworm t i s s u e s i t has been sho\rm i n experiments I I I , IV, V and VI that t h i s r e s u l t s from a c e r t a i n substance or group of substances which the earthworm i s able'to obtain from the humus i n which i t l i v e s . A few f a c t s con-cerning t h i s groY/th-promoting f a c t o r or group of f a c t o r s have been determined. The presence or absence of a- c l i t e l l u m i n the earthworm does not a f f e c t i t s growth-promoting p r o p e r t i e s , A period of 20 days was required f o r crowded depleted earthworms t o secure from f r e s h humus a s u f f i c i e n t supply of growth-promoting m a t e r i a l to cause roughly the same amount of growth i n planarians that was produced by uncrowded de-p l e t e d earthworms a f t e r only 8 days i n the same humus. (See Tables 10, 11 and 12) Also i t was shown that a diet of depleted earthworm produced l e s s f i s s i o n i n the planarians than a diet of lean beef, as w e l l as a greater decrease i n length during a p e r i o d of s t a r v a t i o n than was the case w i t h the l a t t e r . (See Table 8 ) . I t should be noted that during a 3 3 . s i m i l a r period of s t a r v a t i o n planarians p r e v i o u s l y fed on undepleted earthworm decreased somewhat l e s s i n length than those fed lean beef (See Table 7). Hence i t appears that the d i f f e r e n c e between lean beef and earthworm i n the matter of growth-promotion i s e n t i r e l y due to a c e r t a i n substance or group of substances which the earthworm i s able t o extract from humus of a p a r t i c u l a r type. Of the many i n v e s t i g a t i o n s which have been c a r r i e d out on the growth-promoting powers of various d i e t a r y substances, the f o l l o w i n g are t y p i c a l . Bahrs and Wulzen ( '36) i n feeding experiments w i t h a p l a n a r i a n found that s p e c i f i c t i s s u e s of guinea pigs that had been fed on a d i e t containing a l l the vitamins, when fed t o the flatworms, pro-duced a " d i e t a r y disease". However, when c e r t a i n green foods such as kale or a l f a l f a were added to the guinea pigs' diet the r e s u l t i n g t i s s u e s produced good growth i n the p l a n a r i a n s , and without a trace of the " d i e t a r y disease". The authors c a l l e d t h i s growth-promoting f a c t o r i n green f o o d s t u f f s "factor-PL". G-reenberg and Schmidt ( '36) added an ether-soluble f a c t o r which i s present i n l i v e r t o a diet of lean beef and found that t h i s l e d to a marked increase i n growth and f i s s i o n i n P l a n a r i a maculata. They also found that l i t t l e or no growth i n -crease took place when lean beef was supplemented r e s p e c t i v e l y with the known vitamins, unsaturated f a t s or f a t t y a c i d s , or auxin. A l -though the i n v e s t i g a t i o n of the growth-promoting m a t e r i a l i n humus has re c e i v e d no s p e c i a l a t t e n t i o n i n the present work, the evidence on hand seems to substantiate the existence of such a substance or group of substances. Unfortunately, I t was not p o s s i b l e to determine whether the i n -creased growth i n the earthworm-fed planarians might be expressed 3*K wholly or i n part i n terms" of increased metabolic r a t e . The potassium cyanide s u s c e p t i b i l i t y t e s t worked out by C h i l d , Hyman and others would have provided some i n d i c a t i o n of the metabolic rate i n the earthworm-fed and beef-fed animals. However, the lack of time a v a i l a b l e i n which t o secure experience w i t h the technique precluded employment of the t e s t i n the present s e r i e s of experiments. There have been se v e r a l i n v e s t i g a t i o n s of the connection between n u t r i t i o n and metabolic rate i n p l a n a r i a n s . C h i l d ( '15) stated that "the reduction i n s i z e of P l a n a r i a during s t a r v a t i o n i s unquestionably due t o the re-entrance of i t s s t r u c t u r a l m a t e r i a l i n t o metabolism as a source of energy". Hyman ('20) stated that an increase i n metabolism as a consequence of s t a r v a t i o n cannot be expected t o occur u n t i l the p l a n a r i a n a c t u a l l y begins t o use i t s own t i s s u e s f o r food. Hyman ( '19a) found that oxygen consumption of planarians increased markedly a f t e r the i n g e s t i o n of food, and that t h i s increase was maintained only f o r several hours a f t e r feeding, the oxygen consumption then beginning to f a l l . By the f o l l o w i n g day the oxygen consumption decreased again to a marked degree. The work of Robbins and C h i l d ('20) substantiates the l a t t e r f i n d i n g s of Hyman. From the evidence j u s t presented i t may be concluded that i s o l a t e d feedings increase the metabolic r a t e . How-ever, C h i l d ( '15) stated that i f feedings f o l l o w at s u f f i c i e n t l y short i n t e r v a l s growth soon begins i n starved p l a n a r i a n s , and the metabolic r a t e undergoes a gradual decrease as the animal; increases i n s i z e and once more becomes.physiologically o l d e r . From t h i s i t seems reason-able to conclude that since the earthworm-fed planarians are growing at a greater rate than the beef-fed animals, the metabolic rate of the former would be decreasing more r a p i d l y than that of the l a t t e r . I t 35*. might f o l l o w that the metabolic rate of the earthworm-fed animals was lower than that of the beef-fed animals immediately f o l l o w i n g the l a s t i n a c l o s e l y spaced s e r i e s of feedings (See Table 2 ) . Watanabe ( '35) has shown that the time of appearance of eye spots i n E. dorotocephala i s i n d i c a t i v e of the ra t e at which head regener-a t i o n i s proceeding. On t h i s basis i t has been found that the rate of head regeneration i s more r a p i d i n earthworm-fed planarians than i n those fed on beef. (See Tables 4, 5 and 6) Apparently, the earth-worm die t e i t h e r i n d i r e c t l y through i t s e f f e c t upon the metabolic pro-cesses of the planarians proper, or d i r e c t l y by means of the e f f e c t on the regenerate of a", c e r t a i n growth-promoting f a c t o r or group of f a c t o r s contained i n the d i e t and stored i n the o l d t i s s u e s of the p l a n a r i a n , or by means of a combination of both e f f e c t s , i s capable of a c c e l e r a t i n g the r a t e of regeneration i n the head of the organism. Considerable work has been c a r r i e d out by various authors t o show the connection between metabolic ra t e and rate of regeneration. Pourbaix (*32) found that the curve of metabolic rate corresponded to the curve of. regenerative power i n E. dorotocephala. She a r r i v e d at t h i s conclusion on f i n d i n g that parts front the a n t e r i o r region known t o possess a-higher metabolic rate than more p o s t e r i o r parts regener-ate more r a p i d l y than the l a t t e r . Her conclusions receive support from the work of Watanabe (\35)> Abeloos ('27a) and others. Behre ( '18) found that an increase i n temperature r e s u l t s i n an increase i n the metabolic rate of E. dorotocephala. Abeloos Ashowed that an increase i n temperature i n t u r n increased the rate of eye spot appearance i n P l a n a r i a gonocephala. Rulon ( '36) obtained e s s e n t i a l l y the same r e -s u l t s i n E.dorotocephala. Popoff ( '29) discovered that c e r t a i n r e -"36. agents of a s t i m u l a t i n g nature which hasten the oxidative processes i n l i v i n g c e l l s axe capable of s t i m u l a t i n g regeneration i n planarians. I t seems then that an increase i n rate of regeneration i s associated with an increase i n the metabolic rate of the regenerating planarian head. Evidence i n support of the theory that the earthworm diet i s capable i n some way of a c c e l e r a t i n g the metabolic rate i n the regener-a t i n g head w i l l be presented l a t e r i n t h i s d i s c u s s i o n . I t has been shown that f o l l o w i n g on decapitation i n the planarians there was a marked- increase i n the amount of f i s s i o n over that occur-r i n g i n the corresponding unoperated c o n t r o l s . (See Table 3 ) . A l -though t h i s phenomenon has no d i r e c t bearing on the main problem dealt w i t h i n the present work i t i s of s u f f i c i e n t i n t e r e s t to merit i n c l u -s i o n i n the d i s c u s s i o n . C h i l d ('24) states that removal of the head i n planarians favours development of the p o s t e r i o r zooid and f i s s i o n . He found that t h i s was due t o removal of the dominant region i n the organism r e s u l t i n g i n p h y s i o l o g i c a l i s o l a t i o n of the p o s t e r i o r region. In experiment I I , the E j (unoperated earthworm-fed c o n t r o l s ) , ' E J I (decapitated earthworm-fed experimentals), Bj (unoperated beef-fed c o n t r o l s ) , and B J J (decapitated beef-fed Experimentals), were starved f o r a period of 18 days. Length measurements were taken at i n t e r v a l s of a few days. Unfortunately, owing to the i m p o s s i b i l i t y of obtaining an accurate estimate of the length of newly decapitated p l a n a r i a n s , i t was not p o s s i b l e t o determine the e f f e c t of regeneration on the r a t e of length decrease during s t a r v a t i o n , A record of the rate of decrease i n length was obtained, however, i n the case of the unoperated c o n t r o l s . (See Table 7 ) . I t Y/as found that a sudden decrease i n length during the f i r s t few days of s t a r v a t i o n was followed by l e s s and l e s s l o s s of 37. length u n t i l at the end of the second week the rate of length decrease had become n e g l i g i b l e (See P I . V ) . In t h i s connection the work of C h i l d and Hyman must again be con-sidered. C h i l d ('19) and Hyman ('19A) and ( '20) have Investigated the changes In metabolic rate of E. dorotocephala during s t a r v a t i o n . Some of t h e i r r e s u l t s are as f o l l o w s . There i s no l e v e l of "basal" or "standard" metabolism i n E. dorotocephala, but i t s metabolism i s con t i n -uously changing during s t a r v a t i o n . The increase i n metabolic rate due to the i n g e s t i o n of food I s maintained only f o r several hours a f t e r feeding, and then begins to f a l l u n t i l by the.next day i t has again, de-creased markedly, The"metabolic rate continues to f a l l during the f i r s t few days of s t a r v a t i o n , reaching a minimum value w i t h i n the f i r s t , two weeks. The r e s u l t s o u t l i n e d i n the preceding paragraph and contained i n Table 7 coincide with these f i n d i n g s of Hyman and C h i l d . . Hyman ( '20) showed that the weights of starved planarians when taken p e r i o d i c a l l y coincide w i t h the metabolic,condition of the animals at that time. I t may then be concluded that frequent length measurements form a r e l i a b l e i n d i c a t i o n of the metabolic c o n d i t i o n . i n s t a r v i n g E. dorotocephala. Following the l8-day period of s t a r v a t i o n the E j , E J J , Bj and B J J groups were given a s i n g l e feed of earthworm, The r e s u l t i n g lengths have been recorded i n Table 7« The E j group continued t o lose length while the E-r-j- group gained. The B j group continued to lose i n length but the B j j group n e i t h e r l o s t nor gained. In other words, those animals which were regenerating heads were able e i t h e r to maintain t h e i r o r i g i n a l length or t o add t o i t , while the unoperated controls continued to lose l e n g t h . The work of Hyman ( '19b) and Robbins and C h i l d ( '20) o f f e r s an ex-r e -38. p l a n a t i o n f o r t h i s phenomenon. These authors studied the e f f e c t of generation on the metabolism of E. dorotocephala as a whole, They found that when a p l a n a r i a n undergoes regeneration the metabolic rate of the o l d t i s s u e s i s thereby accelerated, i t s rate however i s not as high as that of the regenerated regions. Thus i t i s that the s i n g l e feeding of earthworm i s more productive of growth i n the E J J and B J J groups which have a higher metabolic rate throughout than the E j and Bj planarians. During the 8-day pe r i o d of s t a r v a t i o n f o l l o w i n g the s i n g l e feeding of earthworm the Bjj-group l o s t approximately the percentage of length necessary t o n e u t r a l i z e i t s temporary gain over the Bj c o n t r o l s . A 25~" day period of s t a r v a t i o n was required f o r the same to occur i n the E J J and Ej groups. (See Table 7)• Apparently, then^there i s a compensatory a c c e l e r a t i o n i n l o s s of length i n the regenerating animals which event-u a l l y r e s t o r e s them t o the same length r a t i o w i t h the controls that e x i s t -ed before the s i n g l e feeding. In order to e x p l a i n t h i s phenomenon, i t i s necessary to assume that the s i n g l e feeding of earthworm causes an increase i n the metabolic rate of the regenerating heads, ( i t has p r e v i o u s l y been shown that an e a r t h -worm diet causes an increase i n - r a t e of hea"8 regeneration, and that an increase i n r a t e of head regeneration has been l i n k e d with an increase i n metabolic r a t e ) . I t f o l l o w s from evidence pr e v i o u s l y presented, t h a t , the metabolic r a t e of the o l d p l a n a r i a n t i s s u e s w i l l - i n c r e a s e somewhat due to the stepped up metabolic rate i n the adjacent regenerating t i s s u e s . As long as the earthworm provides an e x t e r n a l supply of food f o r the ex-perimental p l a n a r i a n s , the l a t t e r are able to s a t i s f y t h e i r increased metabolic rate and add to- t h e i r body t i s s u e s . However, when the e x t e r n a l food supply i s withdrawn, the increased metabolic rate i n the head and 3<*. body p e r s i s t s , Loeb ('l6)-has pointed out that " i f regeneration takes place i n pieces which take up no food, the newly formed organs must o r i g i n a t e from m a t e r i a l absorbed from c e l l s of the planarian which are h y d r o l i z e d and whose m a t e r i a l serves as food f o r those c e l l s which grow". The regenerating head secures I t s nourishment from the old t i s s u e s of the body and i n consequence the body shrinks at a greater rate than might have been the case had not the metabolic rate i n the head been ac-ce l e r a t e d by a s i n g l e feeding of earthworm. Ev e n t u a l l y , the s t i m u l a t i n g e f f e c t of the earthworm wears o f f and the metabolic r a t e i n the regener-a t i n g head subsides. Twenty-five days of s t a r v a t i o n are required i n -t h e E J J group to b r i n g the rate of length l o s s on a l e v e l w i t h that i n the Ej c o n t r o l , whereas only 8 days are necessary i n the B J J group. (See Table 7)» This may be explained as f o l l o w s . P o s s i b l y a more perm-anent incres.se i n metabolic rate i s produced i n the regenerating heads of the E J J group than i n the B-rj group. This would have t o be coupled with.the assumption, based on r e s u l t s obtained i n t h i s work regarding the n u t r i t i v e value of the earthworm and lean beef d i e t s , that the E J J group i s able to hold more stores i n reserve than the B j j group. This l a t t e r statement i s borne out to some extent by the statement of Hyman ('20) i n which she points out that the slower l o s s of weight i n P l a n a r i a a g i l i s i s e v i d e n t l y c o r r e l a t e d with i t s greater breadth and thickness and greater supply of food reserves. DISCUSSION. FART II. One week f o l l o w i n g the apparent completion of regeneration of the d i s t a l h a l f of the t a i l i n Hyla r e g i l l a tadpoles, there was no s i g n i -f i c a n t d i f f e r e n c e i n s i z e between the experimental and c o n t r o l groups. (See Table 1 3 ) . However, there was a d e f i n i t e i n d i c a t i o n that a s i g n i -f i c a n t d i f f e r e n c e might have been observed had the s i z e measurements been made e a r l i e r . Such an i n d i c a t i o n was not observed i n data secur-ed two weeks l a t e r . (See Table 14). There are s e v e r a l f a c t o r s which might lead t o the expectation of a temporary lapse i n growth f o l l o w i n g p a r t i a l e x t i r p a t i o n of t h e ' t a i l . The shock occasioned by the operation was s u f f i c i e n t to produce several c a s u a l t i e s . This being the case i t i s not beyond the realm of p o s s i -b i l i t y that the operated tadpoles d i d not feed u n t i l a f t e r they had) r e -covered from the operation. I t was noticed that removal of a part of the t a i l g r e a t l y hampered the movements of the animals. Undoubtedly any feeding that might have taken place would have been i n t e r f e r e d w i t h somewhat on t h i s account. Much e f f o r t and muscular exertion was necess-ary t o produce locomotion a f t e r a p o r t i o n of the t a i l had been cut away. Consequently, there was l i k e l y an increased oxygen metabolism, ?/hich would cause a l l growth to cease, and might even lead to the d e s t r u c t i o n of some of the body t i s s u e s . F i n a l l y , the general metabolism of the ol d t i s s u e s i n the tadpole might have been increased somewhat owing to the presence of the a d j o i n i n g regenerating t i s s u e (See Discussion, Part I , on the e f f e c t of regenerating t i s s u e on adjacent old. t i s s u e s i n Plan-a r i a n s ) , Assuming then that the metabolism throughout the non-feeding hi. tadpole had been accelerated, i t would f o l l o w that catabolism would exceed anabolism, u n t i l feeding began once more. Assuming there had been a cessation or slowing of growth i n the experimental animals, the d i f f e r e n c e i n s i z e between the experimentals and controls had been made up by the t h i r d week f o l l o w i n g the apparent completion of t a i l regeneration. (See Tables 13 and 14). Even between the f i r s t and t h i r d weeks a f t e r the t a i l s had completely regenerated the data provides reason to believe that the experimental animals grew more r a p i d l y than the c o n t r o l s . Thus i t seems that there was a tempor-ary a c c e l e r a t i o n of growth i n the experimentals as compared with the c o n t r o l s , l a s t i n g u n t i l about three weeks f o l l o w i n g the completion of regeneration. Temporary a c c e l e r a t i o n s of growth have been observed i n at l e a s t two cases where regeneration was not involved. Osborne and Mendel ("15) i n t h e i r work on a l b i n o r a t s state that "even after, prolonged periods of suppression of growth, the r a t s can subsequently reach the f u l l s ize c h a r a c t e r i s t i c of t h e i r species. Growth i n the cases r e f e r r e d to i s r e -sumed at a rate normal f o r the size of the animal at the time. I t need not be slow and frequently i t a c t u a l l y exceeds the usual progress". The observations of McCay, D i l l e y , and Crowe11 ( '28) showed that i n brook t r o u t there i s an a c t u a l a c c e l e r a t i o n of grovrth-which p r a c t i c a l l y compensates f o r a period of s t u n t i n g . These r e s u l t s are unexplained. In h i s studies of the e f f e c t s of".starvation' on members of Glass Amphibia, Morgulis ("11, '13) has found that prolonged s t a r v a t i o n has a d e f i n i t e rejuvenating e f f e c t . A f t e r s t a r v a t i o n the animals grew more r a p i d l y , used a l a r g e r percentage of the n u t r i t i o n i n grovrth, and a t t a i n e d a l a r g e r s i z e than those continuously fed. As rejuvenescence occurred i n the"starved tadpoles t h e i r metabolic rate increased. With feeding once more i n progress f o l l o w i n g recovery from the operation, and a surplus of food a v a i l a b l e , greater growth occurred i n the experimentals than i n the c o n t r o l s . However, since the period of f a s t i n g was not as prolonged as i n the experiments of Llorgulis, i t seems probable that the degree of rejuvenescence here was considerably l e s s than that observed by Morgulis i n h i s experimental animals. The consequent accelerated metabolism of the experimental group probably was-not prolonged enough eventually t o produce greater growth i n the -experimentals than i n the c o n t r o l s . A f a c t o r other than rejuvenescence might have contributed to the temporary a c c e l e r a t i o n of growth. I t has been mentioned previously t h a t the presence of a regenerating t a i l w i t h the high metabolic rate found i n a l l p h y s i o l o g i c a l l y young t i s s u e s , might exert an e f f e c t on the remainder of the tadpole which would cause an increase i n i t s metabolic r a t e . I f t h i s were the case, an e f f e c t upon growth s i m i l a r to that produced by rejuvenescence could be expected. P o s s i b l y by one, two or -as long as three weoks a f t e r regeneration had run i t s course i n the t a i l , the increased metabolism i n the re s t of the f r o g would subside to a l e v e l approximating that of the c o n t r o l s , whereupon growth i n the experiment-a l s and c o n t r o l s would proceed at roughly the same r a t e . I t may be concluded then that any a c c e l e r a t i o n i n growth f o l l o w i n g a. period of s t u n t i n g due to the removal of a p o r t i o n of the t a i l i n t a d -poles may be a t t r i b u t e d to the process of rejuvenescence, and p o s s i b l y also t o the e f f e c t of the regenerating t a i l on the metabolism of the a n i -mal as a whole. • Examination of the data i n Tables 15 and l 6 , and a l s o concerning ^3-the time required f o r the appearance of free fore limbs leads to the conclusion that regeneration had no e f f e c t upon the rate of metamor-phosis. The increase i n metabolic rate throughout the tadpole which has been discussed i n the foregoing paragraphs does not n e c e s s a r i l y produce any change i n the rate of metamorphosis, even although i t does a l t e r the rate of growth, This phenomenon might be explained by the work of E t k i n ( '34) w i t h f r o g tadpoles. He noted that a consideration of the l i t e r a t u r e f u r t h e r .strengthens h i s conclusion that "there i s no reason f o r a s c r i b i n g any causative s i g n i f i c a n c e i n metamorphosis t o the supposed metabo1ism-acce1eratihg influen c e of the t h y r o i d . This supposition i t -s e l f i s indeed not adequately supported as applied to l a r v a l or adult f r o g s " . He f u r t h e r pointed out that the metabolism of the b u l l f r o g t a d -pole per u n i t dry weight decreases with age. E t k i n also remarks on the scarceness of l i t e r a t u r e dealing w i t h the metabolic rates i n metamor-phosing amphibia i n general. The f i n d i n g s of E t k i n i n d i c a t e that t h y r o i d accelerates metamorphosis i n tadpoles not by i t s e f f e c t on metabolism but by some other means. I t would appear then that an increase i n meta-bolism such as occurred on account of s t a r v a t i o n and probably on account of regeneration might not m a t e r i a l l y a l t e r the rate of metamorphosis one way or the other. CONCLUSIONS. PART I . The f o l l o w i n g conclusions are the r e s u l t s of a s e r i e s of s i x experiments i n v o l v i n g a t o t a l of 322 specimens of Euplanaria doro-tocephala. 1. A diet of earthworm was more productive of growth and f i s s i o n than a diet of lean heef. 2. There i s evidence t o support the conclusion that the d i f f e r -ence i n growth-promoting and f i s s i o n - p r o d u c i n g power between earthYrorm and lean beef i s a t t r i b u t a b l e t o a substance or group of substances obtained by the earthworm from the humus i n which i t l i v e s . No evidence was secured which might serve t o r e v e a l the metabolic rates i n the earthvrorm-fed and beef-fed animals. 3. Planarians which have received a s u f f i c i e n t number of earth-worm feedings to produce growth and f i s s i o n are able to regener-ate heads more r a p i d l y than those fed f o r a s i m i l a r period on lean beef. This has been a t t r i b u t e d e i t h e r to the d i r e c t e f f e c t of the growth-promoting m a t e r i a l i n the earthworm diet upon the regenerate, or t o the i n d i r e c t e f f e c t of the diet through i t s a c t i o n on the metabolic processes of the o l d t i s s u e s , upon those of the regenerate t i s s u e s , or to a combination of both e f f e c t s . A c o n s i d e r a t i o n of the l i t e r a t u r e revealed that an increase i n r a t e of regeneration i s associated w i t h an increase i n metabolic r a t e , i n the regenerating planarian head. 4. During the f i r s t few days of a period of s t a r v a t i o n , there ¥/as a sudden decrease i n the length of the unoperated pla n a r i a n s , •followed"by a diminishing rate of length decrease u n t i l by the end of the second week the rate of length decrease had become n e g l i g i b l e . These r e s u l t s coincided w i t h the fi n d i n g s of C h i l d and Hyman concerning the changes i n metabolic rate of planarians undergoing s t a r v a t i o n . I t was concluded that length measurements made at frequent i n t e r v a l s provided a r e l i a b l e means of follo?dng the changes i n the metabolic c o n d i t i o n i n s t a r v i n g S, dorotocephala. 5 . Immediately f o l l o w i n g a s i n g l e feeding of earthworm a f t e r an lS-day period of s t a r v a t i o n , those planarians regenerating heads were able e i t h e r ' t o maintain t h e i r o r i g i n a l length or to add t o i t , while the unoperated controls continued t o lose length. This c o i n -cided with the work of C h i l d and Hyman regarding the a c c e l e r a t i o n of the metabolic rate i n o l d t i s s u e s of a pl a n a r i a n owing to the presence on the animal of p h y s i o l o g i c a l l y young regenerating t i s s u e s possessing a higher rate of metabolism. 6 . There appeared t o be a compensatory a c c e l e r a t i o n i n l o s s of length i n the regenerating animals which eventually restored them to the same length r a t i o : . w i t h the controls that e x i s t e d before the s i n g l e feeding of earthworm. This has been explained on the assump-t i o n that an i s o l a t e d feeding of earthworm serves t o increase the metabolic r a t e of the regenerating heads (see Conclusions, #3) which i n t u r n draw:-; h e a v i l y f o r a while on the t i s s u e s of the planarians f o r nourishment, once the ©eternal supply of food has been withdrawn. C 0 N G L U S I 0 N S » PART I I . The f o l l o w i n g conclusions are the r e s u l t s of an experiment i n -v o l v i n g over 90 specimens of Hyla r e g i l l a tadpoles. 1. There was some evidence that a temporary cessation or slowing up of growth had occurred f o l l o w i n g the removal- of the d i s t a l h a l f of the t a i l s i n the experimental tadpoles. Mention was . made of four f a c t o r s which.taken s i n g l y or together might have been, the cause of t h i s phenomenon. 2. There was some evidence that a temporary a c c e l e r a t i o n of growth occurred i n the experimentals, u n t i l the setback i n growth due to the removal of the t a i l s had been compensated and the e x p e r i -mentals and c o n t r o l s were approximately equal i n s i z e . This phenomenon has been a t t r i b u t e d to a process of rejuvenescence during s t a r v a t i o n . A p o s s i b l e second c o n t r i b u t i n g f a c t o r was mentioned, namely the probable a c c e l e r a t i o n produced by physiolog-i c a l l y young regenerating t i s s u e s i n the metabolism of the remain-der of the tadpole. 3« I t appeared that the process of regeneration did not act t o a l t e r the rate of metamorphosis i n the tadpoles. This was ex-p l a i n e d i n terms of the work of .Stkin from which i t seems that metabolic rate i s not the primary f a c t o r i n a c c e l e r a t i n g or slowing down metamorphosis i n tadpoles. 1+7. Abeloos, Marcel, 1927(a). "La v i f e s s e de regeneration de l a t e t e chez P l a n a r i a gonocephala Duge's. Influence du niveau des sec t i o n s " . Gompt. Rend. Acad. S c i . ( P a r i s ) 184(6): 345-347. (3539 B i o l . Absts. Nos. 1-2 Jan.-Feb., 1928). 1927(b). "Sur la. perte de jooids des plana i r e s ( P l a n a r i a gonocephala Duges) en regeneration k clifferentes temp-eratures." Compt. Rend. Soc. B i o l . 96(13):925-926. (3540 B i o l . ' Absts. Hos. 1-2 Jan.-Feb., 1928) Bahrs, A. M. and Wulzen, R. 1936. " N u t r i t i o n a l value f o r planarian worms of vitamin depleted mammalian t i s s u e s . " P h y s i o l . Z o o l . , V o l . 9 , "Pp. 508-529. Behre, E. H. 1918. "An experimental study of acclimation t o temper-ature i n P l a n a r i a dorotocephala." B i o l . B u l l . V o l . 3 5 . Pp. 277-317. Blacher, L. J . j Woronzowa, M. A.; L i o s n e r , L. D. 5 und Samarajew, W. N. (unter Mtwirkung von N. ¥. Bromley, und 0. G. Holzmann) 1931. "Resorptiohsprozesse a l s quelle der Formbildung. V I I . Die mitogenetischen Ausstrahlungen a l s Stimulus des Wachsturns des Vorderbeins b e i der Metamorphose von Rana temporaria." Z e i t s c h r . Wiss. B i o l . Abt. D,Roux' Arch. Entwicklungsmech. Organ. 124(1) :13-8--53. (1927 B i o l . Absts. 1(8). 1935) C h i l d , G. M. 1915. "Senescence and Rejuvenescence". Chicago. 1919. " S u s c e p t i b i l i t y t o l a c k of oxygen during s t a r v -a t i o n i n P l a n a r i a . " Amer. Jour. P h y s i o l . V o l . 49. Pp. 403-419. _ 1924. " P h y s i o l o g i c a l Foundations of Behaviour." New York. Emmett A. D. and A l l e n F. P. 1919. . " N u t r i t i o n a l studies on the growth of f r o g l a r v a e . (Rana p i p i e n s ) " . J . B i o l . Chem. V o l . 38. Pp. 325-344. E t k i n , W. 1934. "The phenomena of"anuran metamorphosis." I I . E. "Oxygen consumption during normal metamorphosis.'' P h y s i o l . Zool. V o l . 7. Pp. 129-148. Greenberg, L. D. and Schmidt, C. L. A. 1936. "Studies on the properties of a growth-promoting f a c t o r f o r P l a n a r i a maculata." Jour. Exp. Zool. V o l . 73. Pp. 375~392. / H i l l i e r , S t . 1928 (1929). "L*influence due jeune sur l a regeneration chez I ' a x o l o t l . " B u l l . I n ternat. Acad. Polonaise S c i , et des L e t t . , c'i. S c i . Math, et Nat. 3B. Zool. 191-217. (11322 B i o l . Absts. 4(4), Apr. 1930). Hyman, L. H. 1919 a. " P h y s i o l o g i c a l studies on P l a n a r i a . " I . "Oxygen consumption i n r e l a t i o n to feeding and sta r v -a t i o n . " Amer. Jour. P h y s i o l . V o l . 49- Pp. 377-402. 1919 b. " P h y s i o l o g i c a l studies on P l a n a r i a . " I I . "Oxygen consumption i n r e l a t i o n to regeneration." Amer. Jour. P h y s i o l . V o l . 50. Pp. 67-8I. h-Q. LIST OF REFERENCE (Cont'd.) 32. 1920. " P h y s i o l o g i c a l studies on P l a n a r i a . " IV. "A f u r t h e r study of oxygen consumption during s t a r v a t i o n . " Amer. Jour. P h y s i o l . V o l . 53. Pp. 399-420. Loeb, J . 1916. "The Organism as a Whole." Met; York. Me Cay, C. M., D i l l e y , W. E.; Crowell, M. F. 1928-29. "Growth rates of brook trou t reared upon'purified rations,, upon dry skim milk d i e t s , and upon feed combinations of cer e a l g r a i n s . " Jour, of N u t r i t i o n . V o l . I . Pp. 233-246. Morgulis, S. 1911. "Studies of i n a n i t i o n i n i t s bearing upon the problem of growth." Arch. F. Entwickelungsrnech., V o l . 1913» "The influence of protracted and i n t e r m i t t e n t f a s t i n g .upon growth." Am. Nat., V o l . XLVII. Morosow, D. C. 1935• "Stimulationseinwirkung des Embryonalextralcts und der. Embryonalgewebe b e i Regenerationsversuchen an amphibien". Roux* Arch. Entwicl:lungsinech. Organ. 133(3)? 310-322. (22249 B i o l . Absts. 10(9) Nov. 1936). Osborne T. B. and Mendel L. B. 1915- "The resumption of growth a f t e r long continued f a i l u r e to grow." J . B i o l . Chern. V o l , 23. Pp. 439-454. p e t t i b o n e , M. and Wulzen R. 1934. " V a r i a t i o n s i n growth-promoting power f o r planarian worms of adult and embryonic t i s s u e s . " P h y s i o l . Zool. V o l . 7. Pp. 192-211. Popoff, Methodi, 1929. "Ueber die Methodik der z e l l s t i m u l a t i o n . " B e r l i n . (13828 B i o l . Absts. 5(5) Hay, 1931.), Pourbaix, N e l l y , 1932. "La p o l a r i t e dans l a regeneration des P l a n a i r e s , " Ann. Soc. Roy. Zool. Belgique. 62:59-69. (7157 B i o l . Absts. 8(3). Mar., 1934.) Robbing, H. L. and C h i l d , 0. M. 1920. "Carbon dioxide production i n r e -l a t i o n to regeneration i n P l a n a r i a dorotocephala." B i o l . B u l l . V o l . 38. Pp.103-122. 1936. "The e f f e c t s of carbon d i o x i d e , the hydrogen-ion, calcium, and experimental c o n d i t i o n i n g on r e c o n s t i t u t i o n i n Euplanaria dorotocephala." P h y s i o l . Zool. Vol.. 9-Pp. 170-203, . f • 1935. "Rate of head development as i n d i c a t e d by time of appearance of eyes i n the r e c o n s t i t u t i o n of Euplanaria dorotocephala." P h y s i o l . Zool., V o l . 8. Pp. 41-64. 1939. " P r i n c i p l e s of Development", New-York. Rulon, O l i n , Watanabe, Y. Weiss, P. 

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