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Reproductive biology of the eastern and least chipmunk Venhuizen, Bradley Austin 1970

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R E P R O D U C T I V E B I O L O G Y O F T H E E A S T E R N A N D L E A S T C H I P M U N K by BRADLEY A. VENHUIZEN B.S., U n i v e r s i t y o f N o r t h D a k o t a , 1966 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENT FOR THE DEGREE OF MASTER OF SCIENCE i n t h e Department o f ZOOLOGY We a c c e p t t h i s t h e s i s as c o n f i r m i n g t o the r e q u i r e d s t a n d a r d THE UNIVERSITY OF BRITISH COLUMBIA March 1970 In presenting this thesis in partial fulfilment of the requirements for an advanced degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree tha permission for extensive copying of this thesis for scholarly purposes may be granted by the Head of my Department or by his representatives. It is understood that copying or publication of this thesis for financial gain shall not be allowed without my written permission. Department The University of British Columbia Vancouver 8, Canada Abstract Eastern and leas t chipmunks from northern Minnesota were studied i n regard to fecundity, age at maturity, timing of reproduction, and changes i n the reproductive organs with age and season. A computer program for discriminate analysis was used to determine r e l a t i ve age of the i n d i v i d u a l animals. T rad i t iona l age indica tors were used as var iab les . The resul t i s a measure of the dispersion of the i n d i v i d u a l animal from a selected control group using a l l variables at once. Subjective decisions are almost eliminated by th is technique. The his tology of the reproductive and accessory organs i s s i m i l a r to that of other sc iu r ids as described by other authors. An apparent difference i s the presence of two very d i s t i n c t i v e areas i n the epididymides. The epithelium of one region has centra l nuc l e i and i s about 31.4 mu, i n height. The epithelium of the other area has basal nuc l e i and i s about 16 mu. i n height. Sperm i s absent from the lumina of the f i r s t tubule type, but abundant i n the lumina of the second tubule type. The chipmunks i n both Oregon and Minnesota had only one breeding season per year which occurred shor t ly after emergence from hibernat ion. Hence juveni les do not breed u n t i l the spring fol lowing the i r b i r t h . A s ign i f i can t change i n ovulation rate of the eastern chipmunk was detected between 1967 and 1968, and for the least - i i i -chipmunk i n Oregon between 1968 and 1969. The rates changed from 7.09 i n 1967 to 4.35 i n 1968 for the eastern chipmunk, and from 4.78 i n 1968 to 6.31 i n 1969 for the least chipmunk. Preimplantation loss and resorption of embryos increased i n the years of lower ovulation rate. - i v -TABLE OF CONTENTS Page T i t l e Page i Abstract i i Table of Contents i v L i s t of Tables v i L i s t of Plates v i i Introduction 1 Mater ia ls and Methods 3 Results 8 Male Reproductive Cycle 8 Juvenile 9 Functional 12 Non-Functional Adult 18 Female Reproductive Cycle 21 Juvenile 22 Estrus . 2 5 Pregnant 27 Lactat ing 30 Anestrus 32 Fecundity 34 Timing of Reproduction 37 Discussion ^2 - v -Male Reproductive Organ Histology 42 Female Reproductive Organ Histology 44 Age at Maturi ty 45 Eutamias minimus and Tamias s t r i a tus 45 Timing of Reproduction 46 Fecundity 48 Conclusions 50 Acknowledgements 58 References 59 - v i -LIST OF TABLES TABLE PAGE I Coeff ic ients for Determining Discriminate 5a Functions I I Ovulation Rates of Least Chipmunks as Indicated by Corpora Lutea Counts 35 I I I Ovulation Rates of Eastern Chipmunks as Indicated by Corpora Lutea Counts 36 - v i i -LIST OF PLATES PLATE PAGE I The Test is and Epididymis 52 I I The Seminal Ves ic le 53 I I I The Prostate and Cowper's Glands 54 IV The Ovary 55 V The Uterus and Vagina 56 VI Special Ovary of the Eastern Chipmunk 57 - 1 -INTRODUCTION D e s p i t e a w i d e s p r e a d d i s t r i b u t i o n , d i u r n a l h a b i t s , and r e ady a c c e s s i b i l i t y , t h e chipmunks (genera Tamias and E u t a m i a s ) have u n t i l r e c e n t l y r e c e i v e d v e r y l i t t l e s c i e n t i f i c a t t e n t i o n . The i n f o r m a t i o n on t h e i r r e p r o d u c t i v e b i o l o g y i s p a r t i c u l a r l y meager. The g e n e r a l b i o l o g y o f t h e e a s t e r n chipmunk, Tamias s t r i a t u s  I l l i g e r , has been c o n s i d e r e d by s e v e r a l a u t h o r s . I n f o r m a t i o n on r e p r o d u c t i o n p r e s e n t e d i s u s u a l l y c o n c e r n e d o n l y w i t h t i m i n g of r e p r o d u c t i o n , number of young p e r f e m a l e b a s e d on embryo c o u n t s , and p r e s e n c e o r absence o f a summer b r e e d i n g s e a s o n . A u t h o r s who have c o m p i l e d s u c h i n f o r m a t i o n a r e C o n d r i n ( 1 9 3 6 ) , B u r t ( 1 9 4 0 ) , Panuska and Wade (1 9 5 7 ) , N e f f and Anthony ( 1 9 6 3 ) , and F o r b e s (1966) . N e f f and Anthony (1963) a r e t h e o n l y i n v e s t i g a t o r s who have d e a l t w i t h t h e h i s t o l o g y o f t h e r e p r o d u c t i v e o r g a n s . They c o n s i d e r e d o n l y the c o n d i t i o n i n t h e male e a s t e r n chipmunk. The l e a s t chipmunk, Eutamias minimus (Bachman), has r e c i e v e d even l e s s a t t e n t i o n t h a n t h e e a s t e r n chipmunk. P a p e r s by C r i d d l e ( 1 9 4 3 ) , M a n v i l l e ( 1 9 4 9 ) , and F o r b e s (1966) c o n t a i n the most i n f o r m a t i o n on t h e g e n e r a l b i o l o g y of t h i s s p e c i e s . R e f e r e n c e s t o t h e i r r e p r o d u c t i v e b i o l o g y c o n c e r n s t h e t i m i n g o f b r e e d i n g , number o f young p e r f e m a l e based on embryo c o u n t s , and p r e s e n c e o r absence o f a summer b r e e d i n g s e a s o n . No i n f o r m a t i o n i s a v a i l a b l e on t h e h i s t o l o g y o f t h e r e p r o d u c t i v e o rgans i n t h i s genus. R e l e v a n t and d e t a i l e d m a t e r i a l on r e p r o d u c t i v e b i o l o g y of s e v e r a l o t h e r members of t h e s c i u r i d f a m i l y i s a v a i l a b l e . Mossman, L a w l a h , -2-and Bradley (1932) published one of the f i r s t studies on the gross morphology of the male s c i u r i d s , including Tamias s t r i a t u s . Mossman, Hoffman, and Ki rkpa t r i ck (1955) and Ki rkpa t r i ck (1955) made excellent studies of the de ta i led structure and changes i n fox and grey s q u i r r e l , of the male reproductive organs. M i l l a r (1968) described the reproduc-t ive biology of the red s q u i r r e l . Moore, C. R. et a l . (1934) and Foster, M. A. (1934) working on the 13-lined ground s q u i r r e l and McKeever (1966) working on the golden-mantled and Belding ground squ i r re l s provide excel lent information on the reproductive biology of hibernating s c i u r i d s . I studied Eutamias minimus neglectus ( J . A. Al len) and Tamias  s t r i a tus griseus Mearns from northern Minnesota to determine changes i n the his tology of the reproductive organs with age and season, timing of reproduction, number of young, age at maturity, and d i f f e r -ences between the two summers of the study. I also col lec ted _E. m. scrutator H a l l and Hat f ie ld i n Oregon to provide more information concerning the length of the breeding season and the early stages of the reproductive h i s to logy . This was necessary since the ear ly events occurred both years i n Minnesota before i t was possible for me to be there. -3-MATERIALS AND METHODS Eutamias minimus neglectus and Tamias s t r i a t u s griseus were c o l l e c t e d i n northern Minnesota from 1 May to 15 September, 1967, and from 20 A p r i l to 1 October, 1968. Almost a l l were taken from Hubbard County, eight miles south of Bemidji. Some were trapped each year from the areas adjacent to Itasca State Park t h i r t y -f i v e miles south of Bemidji. j£.m. scrutator were c o l l e c t e d near Bend, i n Deschutes County, Oregon. Samples were taken from 3 February to 3 A p r i l , 1968, 1 August to 10 August, 1968, 31 October to 4 November, 1968, and from 29 March to 1 May, 1969. A t o t a l of 161 female and 182 male eastern chipmunks and 80 female and 88 male least chipmunks were taken i n Minnesota. Least chipmunks taken i n Oregon numbered 104 females and 113 males. The animals were l i v e trapped i n Sherman f o l d i n g traps using peanut butter as b a i t . A few were also c o l l e c t e d with a .410 shotgun. As soon as possible a f t e r death, usually w i t h i n 5 minutes, the animals were weighed and the standard measurements taken. The testes, epididymides, seminal v e s i c l e s , prostate, and Cowper's glands from the males and the ovaries, u t e r i , and vaginae from the females were removed and placed i n Bouins or AFA f i x a t i v e . Skulls were saved i n a l l cases for use i n aging the animal. A f t e r cleaning the s k u l l s , the i n t e r o r b i t a l breadth and the oc c i p i t o n a s a l length were measured to the nearest tenth of a millimeter using a vernier c a l i p e r . The eyes were removed and placed i n basic 10% formalin. The lenses were used as a parameter i n aging the animal following the dried eye lens technique used by Lord (1959) for aging c o t t o n t a i l r a b b i t s . A f t e r allowing s u f f i c i e n t time -4 -for proper f i x i n g , the lenses were removed from the eyes. A l l the vitreous humor was removed, the lenses were placed i n small v i a l s , and were dried for 48-72 hours i n a 65° oven. Each lens was then weighed to the nearest tenth of a mi l l ig ram on a Sartorius balance. The reproductive organs were processed using standard paraff in embedding techniques, sectioned at 7-8 micra and stained with De la f i e ld ' s hematoxylin and counterstained with eosin. A l l ovaries were s e r i a l l y sectioned. A small sample of testes was s e r i a l l y sectioned to determine the re la t ionships among three d i s t i n c t tubule types i n the epididymides. Aging the animals was done using a computer program for d i s -criminate ana lys i s , (Dixon, 1964). Ind iv idua l chipmunks were compared with control groups of adult and juveni le animals of the same species. The chipmunk was assigned by the computer to e i ther the adult or juveni le group. A p robab i l i t y value showing how closely the i n d i v i d u a l f i t i n the group was computed. Eight variables were used i n the analys is . These were t o t a l , t a i l , hind foot, and ear lengths, s k u l l i n t e r o r b i t a l breadth and occ ip i tonasa l length, t o t a l weight, and weight of the dried eye lens. Control groups were selected on the basis of tooth eruption modified after the c r i t e r i a given by Forbes (1966). Juveniles were those animals i n which the permanent upper fourth premolar had not reached occ lusa l l e v e l . Adults were those animals i n which a l l teeth were at occ lusa l l e v e l . Only those animals which I was cer ta in would f i t these c r i t e r i a were included i n the control groups. Fourteen adults and 21 juveni les of E. m. neglectus, 22 adults and 7 juveniles COEFFICIENTS TABLE I FOR DETERMINING DISCRIMINATE FUNCTIONS Eight Variables _E. m. neglectus C X l X 2 \ X 5 X6 X 7 Adult -2607.38 -2.13 4.48 32.28 10.03 -11.32 167.88 113.19 -2.52 Juvenile -2597.13 -2.14 4.73 32.31 11.44 -11.48 167.11 113.73 -3.47 JL* H' scrutator Adult -1342.22 0.38 5.70 1.73 -5.01 -4.52 -73.78 93.03 0.53 Juvenile -1248.02 0.20 5.37 2.48 -2.57 -4.42 -69.98 89.66 0.09 T. s_. griseus Adult Juvenile -1909.58 0.53 -2.17 34.75 4.58 -8.38 53.03 77.10 -2.20 -1894.76 0.65 -2.40 35.13 4.11 -8.23 53. 72 78.37 -3.18 i U l I TABLE I COEFFICIENTS FOR DETERMINING DISCRIMINATE FUNCTIONS Three V a r i a b l e s E_. m. n e g l e c t u s E_. m. s c r u t a t o r T_. s_. g r i s e u s A d u l t J u v e n i l e A d u l t J u v e n i l e A d u l t J u v e n i l e -384.86 -347.25 -416.92 -348.29 -198.52 -167.42 4.26 4.30 3.15 2.98 0.92 1.21 - 1 . 3 1 -1 .17 2.10 1.89 1.07 0.85 0.28 0.66 0.84 0.49 0.33 -0 .48 of E.m. scrutator , and 11 adults and 32 ju v e n i l e s of T.s.griseus were used as c o n t r o l groups. In some cases values were missing for one or more of the v a r i a b l e s so the p r o b a b i l i t i e s had to be computed using only t o t a l length, t a i l length, and weight of the dried eye lens since no p r o v i s i o n i s made i n the program for missing data. Every animal which had been placed i n the adult or j u v e n i l e category with a p r o b a b i l i t y of more than 95% using a l l eight v a r i a b l e s was always placed i n the same category using only three v a r i a b l e s . Table I gives the formulas for the discriminate functions used i n computing the p r o b a b i l i t i e s f o r each animal. Using eight v a r i a b l e s , 111 out of 122 E_.m. neglectus, 74 out of 80 j^ .m. scrutator, and 199 out of 208 T_. s t r i a t u s were assigned to j u v e n i l e or adult status with p r o b a b i l i t i e s of 95% or more. Using three v a r i a b l e s , 141 out of 154 E_.m. neglectus, 85 out of 125 _E.m. scrutator , and 289 out of 299 T_. s t r i a t u s were assigned to adult or j u v e n i l e status with p r o b a b i l i t i e s of 95% or more. Using only three c h a r a c t e r i s t i c s to age the Oregon chipmunks was quite u n s a t i s f a c t o r y . This i s probably related to the p e r i o d i c nature of the samples taken, and to the very low number of juv e n i l e s trapped. The r e s u l t s obtained would have been more meaningful i f the number of j u v e n i l e s i n the c o n t r o l group would have been larger and taken over a more continuous time span. The sub-adult category of Forbes' was not used because the d i s t i n c t i o n between sub-adult and j u v e n i l e groups i s based on tooth wear and i s very d i f f i c u l t to judge with any accuracy or consistency -7-i n many animals. Forbes' states that sub-adults are animals about 60-100 days old which means that he also considers the animals adult by the time they reach the f i r s t breeding season. No animals were found to breed u n t i l the spring following t h e i r b i r t h so for thi s study the sub-adult category has l i t t l e meaning. -8-RESULTS Male Reproductive Cycle The gross morphology of the male reproductive t r a c t of both genera of chipmunks studied i s e s s e n t i a l l y the same. The absolute s i z e of the testes and accessory organs of the eastern chipmunk are somewhat 1 arger than those of the l e a s t chipmunk. The gross morphology of the reproductive t r a c t of T_. s t r i a t u s as described by Mossman, Lawlah, and Bradley (1932) consists of a pair of testes, s c r o t a l during the breeding season only, a p a i r of tubular winglike seminal v e s i c l e s , a s i n g l e egg-shaped compound tubular prostate, a p a i r of compound tubular Cowper's glands, and bulbar gland formed by the union of the Cowper's ducts i n the base of the penis. A l l but the bulbar gland were considered i n t h i s study. Considerable v a r i a t i o n i n gross s i z e of the testes and accessory organs as w e l l as i n the histology of the organs was detected i n both chipmunks during the course of t h i s study. I established three major stages of reproductive condition to f a c i l i t a t e d e s c r i p t i o n of the male breeding biology. These were the j u v e n i l e , f u n c t i o n a l adult, and non-functional adult. An animal was classed as j u v e n i l e on the basis of aging techniques I gave e a r l i e r and on the general condition of the reproductive t r a c t . Since no animals were found to be i n reproductive condition except i n the spring of the year, this group contained a l l males up to 7 months of age. Animals were classed as f u n c t i o n a l adults on the basis of spermatogenic a c t i v i t y , presence of sperm i n the epididymides, -9-and evidence of secretion i n the accessory glands. Non-functional adults were those which exhibited none of the previous c h a r a c t e r i s t i c s , but which were 7 months of age or older, and which had presumably been i n reproductive condition during the p r i o r spring breeding season. I could see no d i f f e r e n c e i n the histology or gross morphology of the reproductive t r a c t between the l e a s t chipmunks from Minnesota and those from Oregon. Hence, I treat both subspecies of l e a s t chipmunk together. Juvenile Males Eutamias minimus This stage i n the reproductive cycle can usually be determined on the basis of gross morphology alone. The testes are very small and abdominal. The t e s t i s i n a very young animal generally averages about 1.9 by 3.3 mm. i n width and length r e s p e c t i v e l y . Its surface i s smooth and white. No tubules are apparent i n the epididymis. The seminal v e s i c l e s are very small and generally are hidden dorsal to the urinary bladder. The length of a v e s i c l e at this stage i s about 1.5 mm. from the prostate gland to the t i p of the v e s i c l e . The prostate i s also small and i s the base of the V formed by the seminal v e s i c l e s . The width of this organ i s about 1 mm. The p a i r -ed Cowper's glands are also very small being less than 1 mm. i n diameter. They are located on either side of the anus at the base of the t a i l . Often a c e r t a i n amount of d i s s e c t i o n must be done to -10-f i n d these glands i n the f a t , muscle and connective ti s s u e of the area. M i c r o s c o p i c a l l y , the testes are characterized by having very c l o s e l y packed small seminiferous tubules. The lumina of a l l tubules are closed. Spermatogonia, primary spermatocytes, and a few S e r t o l i c e l l s can be seen i n the tubules. The i n t e r s t i t i a l tissue i s quite r e s t r i c t e d ( F i g . l ) . The average diameter of the seminiferous tubules i n 14 j u v e n i l e animals from Minnesota was 43.72 mu. (+2.9). The average diameter of the tubules i n f i v e animals from Oregon was 55.2 mu. (+6.8). The h i s t o l o g i c a l p i c t u r e i n a l l regions of the epididymis i s apparently the same i n th i s age group. The e p i t h e l i a l height i n a l l areas was about 12.2 mu. and was very low cuboidal i n configuration. No sperm are present anywhere i n the epididymis. (Fig.4 ) . The general appearance of the seminal v e s i c l e s i s very character-i s t i c . The tubules are l i n e d with squamosal to cuboidal epithelium and no sec r e t i o n i s present anywhere i n the gland (Fig.8 ) . The epithelium height i s about 10 mu. In the prostate, the tubules are closed completely (Fig.12) . No evidence of secretory a c t i v i t y i s apparent. The Cowper's glands show no secretion, the lumina of the ducts are quite small, and the epithelium i s squamosal to cuboidal (Fig.15) . The amount of connective tissue present i n the gland i s not very large. The e p i t h e l i a l height i s about 10 mu. Tamias s t r i a t u s A t e s t i s from an eastern chipmunk measures about 2.8 by 5.4 mm. i n width and length r e s p e c t i v e l y . The seminiferous tubules of 23 -11-ju v e n i l e s averaged 37.9 mu. (+1.29) i n diameter. (Fig. 1). The h i s t o l o g i c a l p i c t u r e i n a l l other areas i s v i r t u a l l y i d e n t i c a l to that found i n the j u v e n i l e least chipmunk (Figs. 4, 8, 12, 15). In summary, both grossly and micros c o p i c a l l y the measure-ments taken of the t e s t i s and accessory organs of both species are very small. I could see l i t t l e evidence of change towards the fu n c t i o n a l state even i n the j u v e n i l e animals taken l a t e i n the year. The d i f f e r e n c e noted between seminiferous tubule diameters i n the Oregon and Minnesota l e a s t chipmunks may have l i t t l e r e a l meaning. More Minnesota chipmunks were taken e a r l i e r and i n greater numbers therefore bringing the o v e r a l l average to a lower l e v e l . -12-F u n c t i o n a l M a l e s E u t a m i a s minimus The f u n c t i o n a l male can u s u a l l y be a s c e r t a i n e d on t h e b a s i s o f g r o s s morphology o f t h e r e p r o d u c t i v e organs a l o n e . The t e s t e s a r e g r e a t l y s w o l l e n , b e i n g about 5 by 10.5 mm. i n w i d t h and l e n g t h , r e s p e c t i v e l y . They a r e l i n e d by pr o m i n e n t f i n e s t r a i g h t b l o o d v e s s e l s i n t h e t u n i c a a l b u g i n e a . The t e s t e s a r e descended i n t o a d e f i n i t e s c r o t a l s a c w h i c h r e m a i n s q u i t e w e l l f u r r e d t h r o u g h o u t t h e p e r i o d o f b r e e d i n g . A few a n i m a l s t h a t were no l o n g e r f u l l y f u n c t i o n a l had t e s t e s i n the s c r o t a l p o s i t i o n a l s o . T h e r e f o r e t h i s c h a r a c t e r a l o n e i s n o t s u f f i c i e n t t o c l a s s an a n i m a l as f u l l y f u n c t i o n a l . Some t u b u l e s a r e n o t i c e a b l e i n t h e e p i d i d y m i d e s . The s e m i n a l v e s i c l e s a r e p r o m i n e n t , b e i n g w h i t i s h d i s t e n d e d s a c -l i k e s t r u c t u r e s l y i n g d o r s a l t o the u r i n a r y b l a d d e r . The p r o s t a t e l i e s a t t h e ba s e o f t h e p a i r e d s e m i n a l v e s i c l e s . There i s some d i s t e n s i o n i n t h i s o r g a n a l s o , b u t i t i s not n e a r l y as n o t i c e a b l e as i n t h e o t h e r a c c e s s o r y o r g a n s . The p a i r e d Cowper's g l a n d s a r e v e r y s w o l l e n and i n some c a s e s a r e even n o t i c e a b l e e x t e r n a l l y . The s e m i n a l v e s i c l e s a r e about 4-5 mm. l o n g , t h e p r o s t a t e about 3-3.5 mm. i n w i d t h , and t h e Cowper's g l a n d s about 5-6 mm. i n t h e f u l l y f u n c t i o n a l a n i m a l . A b r o a d d u c t c a n be seen on t h e e x t e r n a l s u r f a c e o f t h e Cowper's g l a n d p a s s i n g t o t h e deep s i d e o f the g l a n d t o e n t e r t h e b u l b o f the p e n i s a t i t s b a s e . When t h i s g l a n d i s s l i c e d open t h r o u g h the l a r g e d u c t , a c o n s i d e r a b l e q u a n t i t y o f t h e g l a n d u l a r s e c r e t i o n can - 1 3 -be extruded. This material seems to be much the same as that found i n the fox s q u i r r e l by Mossman, Hoffman, and Ki r k p a t r i c k ( 1 9 5 5 ) . They describe the secretion as white, s l i g h t l y translucent, d u c t i l e , and about the consistency of warmed p a r a f f i n wax. I could not detect any odor coming from the secretion. M i c r o s c o p i c a l l y several c h a r a c t e r i s t i c s can be seen to d i f f e r e n t i a t e the fu n c t i o n a l male. The lumina of the seminiferous tubules are open, and the tubules are f u l l y spermatogenic (Fig. 2 ) . The tubules of 2 3 least chipmunks from Oregon averaged 1 5 6 . 9 8 mu. ( + 7 . 3 2 ) i n diameter. The tubules of 7 f u n c t i o n a l adult least chipmunks from Minnesota averaged 1 2 9 . 8 mu. ( + 1 4 . 7 7 ) i n diameter. The epididymides of the fu n c t i o n a l animal show a very i n t e r e s t -ing h i s t o l o g i c a l p i c t u r e . The vasa e f f e r e n t i a a r i s e s near the upper end of the co n s t r i c t e d c e n t r a l portion of the t e s t i s . There i s a r e l a t i v e l y r e s t r i c t e d area i n which the tubules of the rete t e s t i s and anastomose into those of the vasa e f f e r e n t i a (Fig. 7 ) . The vasa e f f e r e n t i a then loop out to the outside edge of the epididymis, curve up to the c r a n i a l end of the epididymis and blend into the epididymis proper very near the extreme c r a n i a l end of the t e s t i s . In three animals i n which the t e s t i s and accompanying epididymis were s e r i a l l y cross sectioned, the vasa e f f e r e n t i a was found i n the f i r s t 2 . 9 6 mm. of the length of the t e s t i s . In the epididymides proper two h i s t o l o g i c a l l y d i s t i n c t areas can be seen, and there i s some evidence to suggest that there are three funct ional ly d i s t i n c t areas. The tubules into which the vasa efferent ia merge are characterized by a very t a l l somewhat pseudostrat if ied columnar epithelium averaging about 31.4 mu. i n height (F ig . 5) . The nuc le i are ep icen t r i c . The cytoplasm i s highly eos inophi l ic and there appears to be a l i g h t band i n some of the sections which suggests a very act ive secretory epithelium. In most cases no sperm can be detected i n the tubule lumina. Occasionally a few sperm can be detected i n i so la ted groups. It d e f i n i t e l y does not appear to serve as a storage space for sperm. Tubules of th i s type are r e s t r i c t ed to the c r an i a l port ion of the epididymides. In three animals, they were found i n an average of about 1.4 mm. of the length of the t e s t i s and epididymi The area occupied by th i s type of tubule i s usual ly quite small i n any given cross sect ion with the exception of the extreme c r an i a l end of the epididymis where i t may occupy almost the whole cross sec t ion . S l i g h t l y lower i n the c r an i a l end of the epididymides the " t y p i c a l " epididymal tubules are encountered (F ig . 5 ) . They are characterized by having a t a l l columnar epithe lium with basal n u c l e i . The cytoplasm i s again highly ac idoph i l i c Considerable quant i t ies of sperm are found i n the lumina of th i s t i s sue . Tubules of the same h i s t o l o g i c a l appearance are found throughout the length of the epididymis with the exception of the extreme c r a n i a l end. The average length of th i s type of tubule i n three animals s e r i a l l y cross sectioned was 10.9 mm. In some preparations considerably larger quant i t ies of sperm could be found i n the more caudal portions of the epididymides. That th i s -15-c o u l d be an a r t i f a c t o f p r e p a r a t i o n and h a n d l i n g can n o t be r u l e d o u t , b u t I t h i n k t h a t the f r e q u e n c y o f o c c u r e n c e of t h i s phenomenon, n o t o n l y i n t h e t e s t i s w h i c h were s e r i a l l y s e c t i o n e d b u t a l s o i n t h e same r e g i o n i n randomly s e c t i o n e d t e s t i s , w o u l d m i t i g a t e a g a i n s t such a c o n c l u s i o n . I n a d d i t i o n R e i d and C l e l a n d (1957) o b s e r v e d t h e same phenomenon i n the r a t e p i d i d y m i s . The r e a s o n s f o r such a c o n c e n t r a t i o n i n t h e one a r e a o f the e p i d i d y m i s remain o b s c u r e . The d u c t u s d e f e r e n s a r i s e s n e a r the c a u d a l end of each e p i d i d y m i s . When the a n i m a l s a r e f u l l y f u n c t i o n a l , t h i s t u b u l e a l s o c o n t a i n s sperm. The s e m i n a l v e s i c l e s a t t h i s s t a g e have a g r e a t d e a l o f h i g h l y e o s i n i p h i l i c s e c r e t i o n s t o r e d i n v e r y d i s t e n d e d v e s i c l e s ( F i g . 9 ) . The e p i t h e l i u m l i n i n g t h e s e v e s i c l e s i s t a l l columnar w i t h b a s a l n u c l e i and a v e r a g e s about 25.9 mu. i n h e i g h t i n a n i m a l s t a k e n v e r y e a r l y i n the b r e e d i n g s e a s o n . However, i t q u i c k l y changes t o a h e i g h t o f o n l y about 14.8 mu. l a t e r i n the seas o n even though the v e s i c l e s r emain c o m p l e t e l y f i l l e d w i t h s e c r e t i o n . T h i s s e c r e t i o n has some v a c u o l a t i o n p r e s e n t w h i c h may s u g g e s t a f a i r l y h i g h a l c o h o l o r x y l o l s o l u b l e l i p i d c o n t e n t i n the s e c r e t i o n . I n some of the l a s t f u n c t i o n a l males t h e r e i s some i n d i c a t i o n o f a wave of r e g r e s s i o n p a s s i n g f r o m the d i s t a l end o f the s e m i n a l v e s i c l e s t o t he p r o x i m a l end. ( F i g . 1 0 ) . The e p i t h e l i a l h e i g h t and amount of s e c r e t i o n tends t o become s m a l l e r i n t h e s e a r e a s f i r s t . The l o b u l e s of the p r o s t a t e a r e open and a r e b o r d e r e d by c u b o i d a l t o low columnar e p i t h e l i u m m e a s u r i n g about 9.25 mu. i n h e i g h t ( F i g . 1 3 ) . The n u c l e i a r e b a s a l i n a l m o s t a l l c e l l s . The c y t o p l a s m -16-appears s l i g h t l y b a s o p h i l i c and somewhat g r a n u l a r . There i s no s e c r e t i o n s t o r a g e i n the p r o s t a t e . The Cowper's g l a n d s d u r i n g t h i s s t a g e a r e g r e a t l y d i s t e n d e d by a tremendous amount of s e c r e t i o n , ( F i g . 1 6 ) . The main c o l l e c t i o n and s t o r a g e d u c t w h i c h i s v i s i b l e e x t e r n a l l y i s e x p e c i a l l y d i s t e n d e d . B o t h AFA and B o u i n ' s f i x a t i v e s a r e somewhat u n s a t i s f a c t o r y f o r p r e s e r v a t i o n of t h i s g l a n d as they r e n d e r the s e c r e t o r y m a t e r i a l too h a r d f o r s a t i s f a c t o r y s e c t i o n i n g . F r a c t u r i n g of t h e m a t e r i a l u s u a l l y r e s u l t s . The e p i t h e l i u m l i n i n g the main c o l l e c t i o n d u c t and the s e c r e t o r y p o r t i o n s of the g l a n d i s t a l l columnar w i t h b a s a l n u c l e i and measures about 24 mu. The c y t o p l a s m i s somewhat e o s i n o p h i l i c and t h e s e c r e t o r y m a t e r i a l i s v e r y h i g h l y s o . I t i s p o s s i b l e t h a t the s p h e r i c a l g r a n u l e s d e t e c t e d by Mossman, Hoffman, and K i r k p a t r i c k (1955) i n the f o x s q u i r r e l Cowper's s e c r e t i o n a r e a l s o p r e s e n t i n the chipmunk Cowper's g l a n d s . A few p r e p a r a t i o n s gave some i n d i c a t i o n t h a t was the c a s e . However, the h i s t o l o g i c a l t e c h n i q u e s I used were no t comparable and hence I can n o t make d i r e c t c o m p a r i s o n s . Tamias s t r i a t u s The f u n c t i o n a l e a s t e r n male can a l s o be d e t e r m i n e d q u i t e a c c u r a t e l y on the b a s i s of g r o s s morphology a l o n e . The same s w o l l e n c h a r a c t e r o f t h e t e s t e s and a c c e s s o r y organs i s e v i d e n t . However, the e a s t e r n chipmunk male has much l e s s h a i r on the s c r o t a l sac t h a n has t h e l e a s t chipmunk male, and the s a c a l s o becomes q u i t e d a r k l y p i gmented d u r i n g t h e b r e e d i n g s e a s o n . The a v e r a g e s i z e o f the t e s t i s a t t h i s s t a g e i s about 8 by 17 mm. i n w i d t h and l e n g t h , r e s p e c t i v e l y . -17-Th e a c c e s s o r y organs a r e a l s o c o n s i d e r a b l y e n l a r g e d w i t h t h e s e m i n a l v e s i c l e s m e a s u r i n g about 7 mm. i n l e n g t h from p r o s t a t e g l a n d to t i p , t h e p r o s t a t e m e a s u r i n g about 6 mm. i n d i a m e t e r , and t h e Cowper's g l a n d s m e a s u r i n g about 9 mm. i n d i a m e t e r . The h i s t o l o g i c a l p i c t u r e w i t h i n the t e s t i s i s v i r t u a l l y the same as t h a t of t h e l e a s t chipmunk. The s e m i n i f e r o u s t u b u l e s of 18 f u n c t i o n a l a n i m a l s averaged 116.45 mu. (+5.97) i n d i a m e t e r ( F i g . 2 ) . The e p i d i d y m i d e s o f the e a s t e r n chipmunk a r e a l s o v e r y s i m i l a r to t h o s e i n the l e a s t chipmunk ( F i g . 5 ). I n one a n i m a l from w h i c h I s e r i a l l y c r o s s - s e c t i o n e d the t e s t i s and e p i d i d y m i s , the d u c t u s e f f e r e n t i a was f o u n d t h r o u g h 3.8 mm, of the e p i d i d y m i d e s . The p o r t i o n of t h e e p i d i d y m i s w i t h t h e h i g h e s t e p i t h e l i a l h e i g h t (48.9 mu.) was found t h r o u g h 2.5 mm. and the p o r t i o n w i t h i n t e r m i d i a t e e p i t h e i a l h e i g h t (22.1 mu.) was f o u n d t h r o u g h o u t the r e m a i n d e r of the e p i d i d y m i s . The h i s t o l o g y of the a c c e s s o r y organs of t h e e a s t e r n chipmunk i s v i r t u a l l y i n d i s t i n g u i s h a b l e from t h a t seen i n the a c c e s s o r y organs of t h e l e a s t chipmunk ( F i g . 9, 10, 13, 1 6 ) . I n summary, i t can be seen t h a t s e v e r a l c h a r a c t e r i s t i c s a r e u s e f u l i n a s c e r t a i n i n g whether o r n o t a male chipmunk i s r e p r o d u c t i v e l y f u n c t i o n a l . These i n c l u d e t h e t e s t e s b e i n g much e n l a r g e d and i n t h e s c r o t a l s a c , s w o l l e n a c c e s s o r y organs e s p e c i a l l y i n the case of the Cowper's g l a n d s , p r e s e n c e o f sperm i n the t e s t e s , and e p i d i d y m i d e s , s e c r e t i o n p r e s e n t i n t h e s e m i n a l v e s i c l e s and Cowper's g l a n d s and open t u b u l e s i n t h e p r o s t a t e . N o n - F u n c t i o n a l A d u l t Males  Eutamias minimus T h i s s t a g e i n the r e p r o d u c t i v e c y c l e can a l s o be l a r g e l y a s c e r t a i n e d by t h e g r o s s morphology of the t e s t e s and a c c e s s o r y o r g a n s . The t e s t e s , w i t h t h e e x c e p t i o n o f t h o s e w h i c h a r e j u s t b e g i n n i n g t o r e g r e s s , r e t u r n t o t h e a b d o m i n a l c a v i t y and the s c r o t a l s a c becomes u n d e t e c t a b l e . The t e s t e s become b l u i s h , f l a c c i d , and w r i n k l e d i n the e a r l y d e g e n e r a t i n g a n i m a l s and l a t e r becomes smooth, w h i t e and somewhat f i r m . The a v e r a g e s i z e o f t h e t e s t i s a t t h i s s t a g e i s about 2.7 by 5.7 mm. i n w i d t h and l e n g t h , r e s p e c t i v e l y . T u b u l e s o f t h e e p i d i d y m i d e s a r e n o t r e a d i l y v i s i b l e t o t h e naked eye. The s e m i n a l v e s i c l e s become much re d u c e d and a r e u s u a l l y h i d d e n d o r s a l t o the u r i n a r y b l a d d e r . The p r o s t a t e a l s o appears c o n s i d e r a b l y s m a l l e r . Each of t h e s e organs ranges from about 1.5 t o 2.0 mm. i n l e n g t h and d i a m e t e r , r e s p e c t i v e l y . The Cowper's g l a n d s a r e u s u a l l y n o t v i s i b l e e i t h e r w i t h o u t a c e r t a i n amount of c a r e f u l d i s s e c t i o n . They range i n s i z e from about 2.0 t o 2.5 mm. i n d i a m e t e r . M i c r o s c o p i c a l l y the changes a r e e q u a l l y as d r a m a t i c ( F i g . 3 ) . The s e m i n i f e r o u s t u b u l e s become c l o s e l y crowded t o g e t h e r . The l u m i n a o f a l m o s t a l l o f the t u b u l e s become o c c l u d e d w i t h c e l l u l a r d e b r i s . W i t h i n t h e g e r m i n a t i v e e p i t h e l i u m of the s e m i n i f e r o u s t u b u l e s o n l y s p e r m a t o g o n i a , p r i m a r y s p e r m a t o c y t e s , and a few S e r t o l i c e l l s can be seen. The a v e r a g e d i a m e t e r o f the s e m i n i f e r o u s t u b u l e s o f n i n e a n i m a l s of t h i s group from M i n n e s o t a was 57.21 mu. (+6.73). The average d i a m t e r o f the t u b u l e s of s i x a n i m a l s f r o m Oregon was 69.55 mu. (+14.43). -19-The epididymides of the non-functional adult animal i s also very charac te r i s t i c (F ig . 6 ) . There do not seem to be any differences i n the his tology of any region of the epididymis at this stage. The e p i t h e l i a l heights of tubules throughout any given cross sect ion tend to be of about the same magnitude at 15.35 mil. The epithelium of a l l areas varies from almost squamosal to cuboidal i n character. One very charac te r i s t i c point i s the absence of sperm from any port ion of the epididymides. The seminal ves ic les i n th is group decrease to a f rac t ion of the i r former s ize (F ig . 11). No secret ion can be found anywhere i n the gland. The epithelium l i n i n g the ves ic les becomes squamosal to cuboidal , appears heavily nucleated, and measures about 8.2 mu. i n height. A general increase i n the amount of connective t issue present also seems apparent. In the prostate, the tubules close completely (F ig . 14). In this case nucleation i s heavy and lumina are no longer v i s i b l e . There seems to be a general increase i n amount of connective t issue i n this organ a l so . The Cowper's glands show no secret ion at a l l (F ig . 17). The s ize of the lumina of the tubules drops dramatical ly . The epithelium becomes squamosal to cuboidal with very l i t t l e cytoplasm surrounding the nucleus. The height of the epithelium i s about 10.2 mu. Again there seems to be a general increase i n the amount of connective tissue i n the gland. Tamias s t r i a tus Grossly and microscopical ly th is group i s very s i m i l a r to the least chipmunk a l so . An average t e s t i s i n th is group i s 4 by 10 mm. -20-i n w i d t h and l e n g t h , r e s p e c t i v e l y . Measurements of the a c c e s s o r y o rgans of the e a s t e r n chipmunk a l s o i n the 2.0 t o 2.5 mm. r a n g e . The s e m i n i f e r o u s t u b u l e s o f 20 a n i m a l s a v e r a g e d 56.08 mu. (+7.84) i n d i a m e t e r . No e v i d e n c e c o u l d be seen f o r d i s t i n g u i s h i n g between a r e a s o f t h e e p i d i d y m i d e s i n t h i s s p e c i e s e i t h e r ( F i g . 3,6 ) . The a c c e s s o r y organs were a g a i n s i m i l a r i n v i r t u a l l y e v e r y d e t a i l t o t h e p i c t u r e p r e s e n t e d by the l e a s t chipmunk ( F i g . 14, 1 7 ) . I n summary, t h e n o n - f u n c t i o n a l a d u l t male o f b o t h s p e c i e s i s c h a r a c t e r i z e d by h a v i n g a b d o m i n a l t e s t e s ( e x c e p t i n t h e v e r y e a r l i e s t d e g e n e r a t i n g a n i m a l s ) , s m a l l s i z e o f a l l r e p r o d u c t i v e o r g a n s , s m a l l t i g h t l y p acked s e m i n i f e r o u s t u b u l e s w i t h c l o s e d l u m i n a , squamosal t o c u b o i d a l v e s i c l e s , and Cowper's g l a n d s , no s e c r e t i o n i n any g l a n d s , and c l o s e d l o b u l e s i n the p r o s t a t e . - 2 1 -Female R e p r o d u c t i v e C y c l e The f e m a l e r e p r o d u c t i v e t r a c t o f t h e chipmunk has n o t h e r e -t o f o r e been a d e q u a t e l y d e s c r i b e d . N e f f and Anthony (1963) make b r i e f r e f e r e n c e t o the g r o s s morphology o f t h e r e p r o d u c t i v e t r a c t o f the f e m a l e Tamias s t r i a t u s . Mossman (1966) gave a g e n e r a l d e s c r i p t i o n o f t h e h i s t o l o g y o f t h e r o d e n t o v a r y based on o b s e r v a t i o n s o f s e v e r a l s c i u r i d and m u r o i d r o d e n t s i n c l u d i n g T_. s t r i a t u s . F i v e c a t e g o r i e s have been e s t a b l i s h e d i n t h i s s t u d y t o f a c i l i t a t e d e s c r i p t i o n of t h e h i s t o l o g y of the f e m a l e r e p r o d u c t i v e o r g a n s . These a r e j u v e n i l e , e s t r o u s , a n e s t r o u s , p r e g n a n t , and l a c t a t i n g f e m a l e s . The j u v e n i l e c a t e g o r y i s b a s e d on my c r i t e r i a p r e s e n t e d e a r l i e r f o r a g i n g t h e a n i m a l s . The e s t r o u s and a n e s t r o u s f e m a l e s were so c l a s s e d on the b a s i s of h i s t o l o g i c a l v a r i a t i o n i n the o r g a n s . P r e g n a n t a n i m a l s were t h o s e i n w h i c h v i s i b l e s w e l l i n g was d e t e c t e d i n the u t e r u s , and l a c t a t i n g a n i m a l s were t h o s e i n w h i c h v i s i b l y a c t i v e mammary t i s s u e was p r e s e n t . J u v e n i l e Females Eutam i a s minimus E x t e r n a l l y t h e j u v e n i l e f e m a l e shows no s i g n o f r e p r o d u c t i v e a c t i v i t y . The v u l v a i s s m a l l and does n o t p r o t r u d e , and t h e n i p p l e s can n o t be seen w i t h o u t an e f f o r t . I n t e r n a l l y , t h e whole r e p r o d u c t i v e t r a c t i s q u i t e s m a l l . The o v a r i e s a r e u s u a l l y n o t v i s i b l e as th e y a r e c o v e r e d by t h e s u r r o u n d i n g b u r s a . When th e y a r e e x p o s e d , the o v a r i e s can be seen as s m a l l smooth w h i t e b o d i e s . The average d i a m e t e r o f 18 o v a r i e s from n i n e a n i m a l s was about 0.9 mm. The average d i a m e t e r o f t h e u t e r i was about 0.8 mm., and t h a t o f t h e v a g i n a e about 0.4 mm. The u t e r u s and v a g i n a show no e v i d e n c e o f any t u r g i d i t y . M i c r o s c o p i c a l l y , t h e o v a r y o f t h i s group i s t y p i c a l o f t h e g e n e r a l r o d e n t o v a r y as d e s c r i b e d by Mossman (1966). I t has a l a r g e number o f naked ova i n the c o r t e x and many p r i m a r y f o l l i c l e s ( F i g . 1 8 ) . Some of the l a t e r i n f a n t i l e o v a r i e s do d e v e l o p s e c o n d a r y f o l l i c l e s . The a v e r a g e g r e a t e s t d i a m e t e r s o f 26 d e v e l o p i n g f o l l i c l e s f r o m s i x j u v e n i l e s was 120.6 mu. by 91.3 mu. The s m a l l e s t d e v e l o p i n g f o l l i c l e s were seen i n t h e f i r s t j u v e n i l e caught i n 1967. One such f o l l i c l e s measured o n l y 27.8 mu. by 25.9 mu. The l a s t j u v e n i l e t a k e n i n 1967 h a d t h e l a r g e s t f o l l i c l e s of t h o s e measured. I n no case were any a n i m a l s c l a s s e d as j u v e n i l e s f ound t o have any c o r p o r a l u t e a o r G r a a f i a n f o l l i c l e s p r e s e n t . The u t e r u s of t h e j u v e n i l e c o n s i s t s o f t h r e e c o n c e n t r i c bands of t i s s u e ( F i g . 2 4 ) . These a r e t h e a d v e n t i a l l a y e r w h i c h i s r e l a t i v e l y -23-t h i n , a l a y e r o f smooth muscle i n b o t h l o n g i t u d i n a l and c i r c u l a r b u n d l e s w h i c h i s termed the myometrium, and an endometrium c o n s i s t -i n g o f a mucous membrane l i n i n g the lumen of t h e u t e r u s . W i t h i n the endometrium v a r y i n g numbers of e n d o m e t r i a l g l a n d s o c c u r . These a r e formed as i n v a g i n a t i o n s o f the e p i t h e l i u m l i n i n g the u t e r i n e lumen. The j u v e n i l e u t e r u s has a f a i r l y t h i n endometrium and myometrium. The myometrium a v e r a g e d about 45 mu. i n t h i c k n e s s i n s i x a n i m a l s and t h e endometrium a v e r a g e d about 110 mu. The number and d i s t r i b u t i o n o f e n d o m e t r i a l g l a n d s was h i g h l y v a r i a b l e . I n a l m o s t a l l cases the l u m i n a o f s u c h g l a n d s were c l o s e d . The e p i t h e l i u m o f b o t h t h e g l a n d s and l i n i n g o f the lumen of the u t e r u s i s c u b o i d a l w i t h v e r y l a r g e n u c l e i . The v a g i n a i s a l s o a s i m p l e t u b u l a r s t r u c t u r e w i t h t h e i n n e r l a m i n a p r o p r i a of dense c o n n e c t i v e t i s s u e c o v e r e d by a squamosal e p i t h e l i u m , m i d d l e smooth m u s c l e l a y e r w i t h b o t h l o n g i t u d i n a l and c i r c u l a r m uscle b u n d l e s , and an o u t e r a d v e n t i t i a l l a y e r ( F i g . 2 7 ) . I n the j u v e n i l e s a l l l a y e r s a r e q u i t e s m a l l . There i s v e r y l i t t l e s t r a t i f i c a t i o n of t h e e p i t h e l i a l l i n i n g and no i n d i c a t i o n o f c o r n i f y i n g l a y e r s : on t h e s u r f a c e o f t h e e p i t h e l i u m . Tamias s t r i a t u s The s i m i l a r i t y i n h i s t o l o g y of r e p r o d u c t i v e organs w h i c h e x i s t s between male l e a s t and e a s t e r n chipmunks i s a l s o e v i d e n t between f e m a l e l e a s t and e a s t e r n chipmunks. The average s i z e of 15 j u v e n i l e o v a r i e s was about 1.8 mm., t h e a v e r a g e d i a m e t e r of the u t e r i was about 0,6 mm., and the a v e r a g e v a g i n a l d i a m e t e r was about 0.8 mm. A g a i n t h e s e measurements a r e from f i x e d specimens. -24-No differences of any consequence ex is t i n the h i s t o l o g i c a l appearance of any of the reproductive organs of the eastern chipmunk as compared to the appearance i n the least chipmunk. (F ig . 24, 27). -25-E s t r o u s Females E u t a m i a s minimus The e x t e r n a l f e a t u r e s and g r o s s morphology of t h e e s t r o u s a n i m a l a r e o f t e n enough t o d i s t i n g u i s h t h i s group. The v u l v a i s r e d , p r o t r u d i n g , and u s u a l l y open. I n t e r n a l l y t h e r e p r o d u c t i v e t r a c t i s c o n s i d e r a b l y s w o l l e n a l s o . The o v a r i e s o f t e n have a g r a n u l a r a p p e a r a n c e due t o t h e b u l g i n g G r a a f i a n f o l l i c l e s . I t i s r a r e l y n e c e s s a r y t o remove t h e s u r r o u n d i n g b u r s a b e f o r e t h i s l a s t f e a t u r e can be c l e a r l y s e e n . The r e l a t i v e s i z e s o f t h e o r g a n s i n an e s t r o u s a n i m a l a r e a d i a m e t e r o f about 2.25 mm. f o r t h e o v a r y , 1.6 mm. f o r t h e u t e r u s , and about 1.75 mm. f o r the v a g i n a . M i c r o s c o p i c a l l y , t h e o v a r i e s a r e c h a r a c t e r i z e d by h a v i n g v e r y l a r g e , s w o l l e n f o l l i c l e s w i t h c o n s i d e r a b l e f l u i d i n t h e a n t r a ( F i g . 1 9 ) . No c o r p o r a l u t e a c a n be f ound i n t h e s e o v a r i e s . The a v e r a g e l a r g e s t d i a m e t e r s o f 23 f o l l i c l e s f rom f o u r E. m. s c r u t a t o r was 455.4 mu. by 374.3 mu. These f o l l i c l e s a r e n e a r l y f o u r t i m e s as l a r g e as t h o s e found i n t h e a v e r a g e j u v e n i l e a n i m a l . The u t e r u s o f t h e e s t r o u s f e m a l e shows a g e n e r a l i n c r e a s e i n t h e t h i c k n e s s o f b o t h t h e myometrium and the endometrium ( F i g . 2 5 ) . The a v e r a g e t h i c k n e s s o f t h e myometrium i s about 220 mu. and t h e endometrium i s about 450 mu. t h i c k . The e p i t h e l i u m l i n i n g b o t h t h e lumen and t h e e n d o t h e l i a l g l a n d s towards columnar w i t h some p s e u d o s t r a t i f i c a t i o n . The l u m i n a o f most e n d o m e t r i a l g l a n d s a r e open. There a r e i n d i c a t i o n s o f an i n c r e a s e i n b o t h number and -26-c o m p l e x i t y o f g l a n d s , b u t r e s u l t s a r e so v a r i a b l e t h a t d i r e c t c o m p a r i s o n w i t h o t h e r groups i s i m p o s s i b l e . There does n o t seem t o be a s u b s t a n t i a l i n c r e a s e i n t h e v a s c u l a r i z a t i o n o f any g i v e n a r e a . The v a g i n a i s a v e r y good i n d i c a t o r of the e s t r o u s a n i m a l ( F i g . 2 8 ) . The l a m i n a p r o p r i a and smooth muscle l a y e r s do n o t i n c r e a s e i n t h i c k n e s s t o any g r e a t e x t e n t . The e p i t h e l i u m becomes h e a v i l y c o r n i f i e d , and i t a l s o becomes i n c r e a s i n g l y s t r a t i f i e d . I n many a n i m a l s , the l u m i n a become almo s t b l o c k e d w i t h d e b r i s s l o u g h e d from the l i n i n g e p i t h e l i u m . Tamias s t r i a t u s No a n i m a l s were t a k e n w h i c h were j u d g e d t o be i n e s t r u s . -27-P r e g n a n t Females Eutamias minimus A l t h o u g h some e r r o r may r e s u l t from d e f i n i n g t h i s group as t h o s e a n i m a l s w i t h v i s i b l e s w e l l i n g i n the u t e r u s , I f e e l t h e e r r o r was v e r y s m a l l i n t h i s s t u d y . I t r a p p e d o n l y t h r e e females w h i c h may have r e c e n t l y o v u l a t e d and y e t showed no s i g n of s w e l l i n g i n t h e u t e r u s . How soon a f t e r o v u l a t i o n and f e r t i l i z a t i o n s u c h s w e l l i n g appears was n o t d e t e r m i n e d . E x t e r n a l l y the o n l y n o t i c e a b l e c h a r a c t e r i s t i c o f t h i s group i s t h a t the v u l v a becomes f l a c c i d and does n o t p r o t r u d e as n o t i c e a b l y as i n the e s t r o u s f e m a l e . I n t e r n a l l y some g r o s s m o r p h o l o g i c a l c h a r a c t e r s a r e a p p a r e n t . The o v a r i e s of t h e s e a n i m a l s a r e d e f i n i t e l y g r a n u l a r and o c c a s i o n a l l y b l o o d c l o t s i n t h e c o r p o r a l u t e a w h i c h appear as d a r k brown s p o t s can be seen on the s u r f a c e o f the o v a r y . The s p o t s a r e e s p e c i a l l y n o t i c e a b l e i n a v e r y r e c e n t l y p o s t o v u l a t o r y a n i m a l as j u d g e d on the b a s i s o f s i z e o f s w e l l i n g i n t h e u t e r u s . The e n l a r g e d nodes i n a r e a s o f i m p l a n t a t i o n i n the u t e r u s a r e o f c o u r s e most n o t i c e a b l e . The v a g i n a becomes f l a c c i d and s h r i n k s somewhat i n s i z e . The a v e r a g e d i a m e t e r of 15 o v a r i e s was about 2.2 mm. and the a v e r a g e d i a m e t e r from s e v e n v a g i n a e was about 1.8 mm. M i c r o s c o p i c a l l y , t h e o v a r i e s a l o n e a r e d i f f i c u l t t o d i s t i n g u i s h f r o m t h o s e o f l a c t a t i n g o r even e a r l y a n e s t r o u s f e m a l e s ( F i g . 2 0 ) . The o n l y e x c e p t i o n i s when l a r g e b l o o d c l o t s a r e formed i n t h e c o r p o r a l u t e a . The a n i m a l s i n w h i c h t h e s e were found were a l l i n - 2 8 -the e a r l y s t a g e s of p regnancy. The average l a r g e s t d i a m e t e r s o f 2 8 c o r p o r a l u t e a from f i v e a n i m a l s was 7 6 5 . 2 mu. by 6 1 0 . 4 mu. L a r g e d e v e l o p i n g and a t r e t i c f o l l i c l e s were n o t i c e d i n the o v a r i e s o f most p r e g n a n t f e m a l e s . The u t e r i o f p r e g n a n t a n i m a l s i s somewhat s w o l l e n . V a s c u l a r -i z a t i o n i s i n c r e a s e d and some s e p e r a t i o n i s u s u a l l y o b s e r v e d between t h e endometrium and myometrium. The myometrium average about 3 4 5 mu. and t h e endometrium about 1 8 2 mu. i n t h i c k n e s s . The e p i t h e l i u m approaches columnar i n b o t h the u t e r i n e l i n i n g and t h e l i n i n g of t h e e n d o m e t r i a l g l a n d s . The v a g i n a of the p r e g n a n t a n i m a l v a r i e s l i t t l e i n h i s t o l o g y from t h a t seen i n the j u v e n i l e e x c e p t i n s i z e ( F i g . 2 9 ) . The e p i t h e l i u m a g a i n becomes s t r a t i f i e d squamous of o n l y two o r t h r e e l a y e r s w i t h no n o t i c e a b l e c o r n i f i c a t i o n o f the o u t e r l a y e r s . No d e b r i s i s o b s e r v e d i n the v a g i n a l lumen i n p r e g n a n t a n i m a l s . Tamias s t r i a t u s Only one f e m a l e e a s t e r n chipmunk was t a k e n w h i c h was v i s i b l y p r e g n a n t . The o v a r i e s of t h i s a n i m a l a r e somewhat d i f f e r e n t f rom t h o s e i n the l e a s t chipmunk. F i r s t t h e r e i s c o n s i d e r a b l y more v a s c u l a r i z a t i o n i n t h e body o f t h e o v a r y . S e c o n d l y , t h e c e n t e r s o f t h r e e o f the c o r p o r a l u t e a c o n t a i n an a r e a w h i c h appears t o be u n d e r g o i n g an i n v a s i o n by c o n n e c t i v e t i s s u e . T h i s c o n n e c t i v e t i s s u e a r e a i s somewhat d i s o r i e n t e d w i t h much s m a l l e r n u c l e i t h a n i n t h e s u r r o u n d i n g l u t e a l t i s s u e . I n one c o r p o r a l u t e u m t h i s a r e a i s a p p r o x i m a t e l y 1 5 0 mu, by 4 1 2 mu. a t i t s g r e a t e s t e x t e n t . -29-F i n a l l y t h e o v a r y i s somewhat l a r g e r o v e r a l l m e a s u r i n g about 3 mm. i n d i a m e t e r . S e v e r a l l a r g e f o l l i c l e s , some w i t h a n t r a w e l l formed, can be seen r e g r e s s i n g i n t h e s e o v a r i e s a l s o . The u t e r u s of t h i s a n i m a l i s much l i k e t h a t seen i n p r e g n a n t l e a s t chipmunks. The e p i t h e l i u m of the u t e r i n e l i n i n g and of t h e e n d o m e t r i a l g l a n d s i s c u b o i d a l and about 14.15 mu. i n h e i g h t . The endometrium ranges i n t h i c k n e s s from about 65-80 mu. and the myometrium from about 250-300 mu. The v a g i n a i s about 3.5 mm. i n d i a m e t e r ( F i g . 2 9 ) . The squamous e p i t h e l i u m i s two o r t h r e e c e l l l a y e r s t h i c k , and t h e r e i s no e v i d e n c e o f any c o r n i f i c a t i o n o f the o u t e r l a y e r s o r d e b r i s i n the v a g i n a l lumen. -30-L a c t a t i n g Females Eutamias minimus The s i n g l e e x t e r n a l c h a r a c t e r w h i c h s u f f i c e s t o i d e n t i f y t h i s group i s the p r e s e n c e o f m i l k i n the mammary t i s s u e . M a n i p u l a t i o n can p r o d u c e a s m a l l amount o f m i l k a t the n i p p l e f o r v e r i f i c a t i o n . The n i p p l e s become s l i g h t l y e l o n g a t e d and a h a i r l e s s a r e a d e v e l o p s around them. The v u l v a i s a g a i n s m a l l and i n c o n s p i c u o u s . I n t e r n a l l y t h e r e a r e few marked changes e x c e p t f o r absence o f s w e l l i n g i n the u t e r u s w h i c h s e r v e t o d i s t i n g u i s h t h i s group from t h o s e p r e c e d i n g . The o v a r i e s appear somewhat g r a n u l a r due t o s l i g h t l y p r o t r u d i n g c o r p o r a l u t e a , b u t brown s p o t s due t o b l o o d i n the c o r p o r a l u t e a was n e v e r o b s e r v e d i n t h i s group. The o v a r y averages about 1.5 mm. i n d i a m e t e r i n t h i s group and the v a g i n a i s about 0.8-0.9 mm. i n d i a m e t e r . M i c r o s c o p i c a l l y , the o v a r i e s a r e a g a i n v e r y h a r d to c l a s s i f y by t h e m s e l v e s . ( F i g . 21). D e v e l o p i n g and a t r e t i c f o l l i c l o f v a r i o u s s i z e s a r e p r e s e n t , i n c l u d i n g a few w h i c h have reached t h e s t a g e of antrum f o r m a t i o n . C o r p o r a l u t e a were n e v e r found w i t h b l o o d c l o t s i n t h e i r c e n t e r s i n t h i s group, A few were found w i t h some e v i d e n c e o f i n v a s i o n by c o n n e c t i v e t i s s u e i n t h e i r c e n t e r s , b u t t h e s e a r e a s were always v e r y s m a l l and i n d i s -t i n c t . The a v e r a g e g r e a t e s t d i a m e t e r s of 33 c o r p o r a l u t e a from s i x a n i m a l s was 738.6 mu. by 891.4 mu. A l t h o u g h t h e s e d i a m e t e r s a r e somewhat l a r g e r t h a n t h o s e measured f o r p r e g n a n t a n i m a l s the d i f f e r e n c e i s n o t s i g n i f i c a n t . - 3 1 -The u t e r u s of a l a c t a t i n g f e m a l e remains somewhat e n l a r g e d ( F i g , 2 6 ) . The i n c r e a s e d v a s c u l a r i z a t i o n n o t i c e d i n the p r e g n a n t u t e r u s i s m a i n t a i n e d t o a l a r g e e x t e n t . The t h i c k n e s s of t h e myometrium i s about 415 mu., and the t h i c k n e s s of the endometrium i s about 190 mu. Most of the e n d o m e t r i a l g l a n d l u m i n a a r e open, and the e p i t h e l i u m l i n i n g them and the lumen of the u t e r u s i s c u b o i d a l . The v a g i n a of t h i s group v a r i e s l i t t l e from t h a t found i n a p r e g n a n t a n i m a l ( F i g . 2 9 ) . Tamias s t r i a t u s B o t h e x t e r n a l l y and i n t e r n a l l y t h e e a s t e r n f e m a l e s of t h i s group v a r y l i t t l e f rom t h e l e a s t chipmunk f e m a l e s j u s t d e s c r i b e d . The e a s t e r n chipmunk, however, has o v a r i e s t h a t a v e r a g e about 2.7 mm. i n d i a m e t e r , v a g i n a e about 2.0-2.5 mm. i n d i a m e t e r , a n d u t e r i about 0.7-0.8 mm. i n d i a m e t e r . M i c r o s c o p i c a l l y , the h i s t o l o g y of a l l r e p r o d u c t i v e organs i s t h e same as d e s c r i b e d f o r the l e a s t chipmunk w i t h t h e e x c e p t i o n of the c o r p o r a l u t e a ( F i g . 22, 26, 2 9 ) . A l l the c o r p o r a l u t e a of t h i s group have a v e r y d i s t i n c t h i g h l y e o s i n o p h i l i c c e n t r a l a r e a w h i c h appears to be an a r e a o f c o n n e c t i v e t i s s u e . The a r e a i s somewhat more o r g a n i z e d and more condensed th a n the a r e a seen i n the p r e g n a n t e a s t e r n chipmunk. The average a r e a o c c u p i e d by t h i s c o n n e c t i v e t i s s u e a r e a i s about 90 mu. by 170 mu. The a v e r a g e g r e a t e s t d i a m e t e r s o f 30 c o r p o r a l u t e a from f i v e a n i m a l s was 522 mu. by 639.5 mu. -32-A n e s t r o u s Females Eutam i a s minimus The e x t e r n a l appearance o f t h e r e p r o d u c t i v e p a r t s of the a n e s t r o u s f e m a l e d i f f e r from t h o s e seen i n the j u v e n i l e o n l y i n t h a t the n i p p l e s o c c a s i o n a l l y remain s l i g h t l y e l o n g a t e d and brown t i n g e d . G r o s s l y , the r e p r o d u c t i v e t r a c t i s i n d i s t i n g u i s h a b l e from t h a t o f the j u v e n i l e . The o v a r i e s show a s i m i l a r h i s t o l o g i c a l appearance as t h o s e i n the p r e v i o u s two groups ( F i g . 2 3 ) . I n the l a t e r a n e s t r o u s a n i m a l s the c o r p o r a l u t e a b e g i n t o t a k e even l e s s s t a i n t h a n u s u a l and show some s i g n s o f breakdown such as v a c u o l a t i o n . The c o r p o r a l u t e a undergo a c o n s i d e r a b l e r e d u c t i o n i n s i z e . One a n i m a l t a k e n l a t e i n the f a l l had c o r p o r a l u t e a w h i c h measured about 400 mu. by 313 mu. i n average g r e a t e s t d i a m e t e r s . The o v a r i e s i n e a r l i e r a n e s t r o u s f e m a l e s a r e v i r t u a l l y i d e n t i c a l t o t h o s e of t h e l a c t a t i n g a n i m a l s . I n b o t h o v a r i e s w i t h and w i t h o u t c o r p o r a l u t e a p r e s e n t , f o l l i c l e s can be found up t o the s t a g e of a n t r a f o r m a t i o n and a l l s t a g e s of a t r e s i a . The u t e r u s of an a n e s t r o u s a n i m a l i s i n t e r m e d i a t e i n s i z e between t h a t of a j u v e n i l e and t h a t of a p r e g n a n t o r l a c t a t i n g a n i m a l . The a v e r a g e t h i c k n e s s of t h e myometrium i s about 70 mu. and t h a t of the endometrium i s about 120 mu. The e p i t h e l i u m l i n i n g the lumen o f t h e u t e r u s and e n d o m e t r i a l g l a n d s i s c u b o i d a l , and t h e l u m i n a of most o f the e n d o m e t r i a l g l a n d s a r e c l o s e d . The v a g i n a i s i n much the same c o n d i t i o n as t h a t found i n -33-p r e g n a n t o r l a c t a t i n g a n i m a l s ( F i g . 2 9 ) . A s l i g h t d e c r e a s e i n s i z e seems to be the o n l y change. Tamias s t r i a t u s A g a i n the same d e s c r i p t i o n g i v e n f o r the l e a s t chipmunk f i t s t he e a s t e r n as w e l l . The o v a r i e s i n t h i s group average about 2.4 mm. i n d i a m e t e r and the v a g i n a e about 1.7 mm. i n d i a m e t e r . L i t t l e can be added t o h i s t o l o g i c a l d e s c r i p t i o n s a l r e a d y g i v e n f o r t h e r e p r o d u c t i v e organs o f the l e a s t chipmunk ( F i g . 2 9 ) . The c e n t r a l c o n n e c t i v e t i s s u e a r e a seems t o remain about the same m e a s u r i n g about 120 mu. by 140 mu. i n t h i s group ( F i g . 2 3 ) . The c e n t r a l a r e a does become more h i g h l y e o s i n o p h i l i c . The av e r a g e d i a m e t e r s o f t h e c o r p o r a l u t e a drop c o n s i d e r a b l y . The av e r a g e g r e a t e s t d i a m e t e r s f o r 24 c o r p o r a l u t e a from f o u r a n i m a l s was 402 mu. by 470 mu. -34-F e c u n d i t y Three methods were used t o d e t e r m i n e t h e number o f young a g i v e n a n i m a l p r o d u c e d . These were c o r p o r a l u t e a c o u n t s , i m p l a n t a t i o n s c a r c o u n t s , and number o f embryos. Each of t h e s e has a t l e a s t one d i s a d v a n t a g e . C o u n t i n g t h e number o f embryos i s u n d o u b t e d l y t h e most a c c u r a t e means o f a s s e s s i n g t h e p r o b a b l e number o f young. U n f o r t u n a t e l y r e l a t i v e l y few a n i m a l s were t a k e n w h i c h were p r e g n a n t , and a l s o i t i s d i f f i c u l t t o a c c o u n t f o r r e s o r p t i o n . I m p l a n t a t i o n s c a r c o u n t s a r e p r o b a b l y l e a s t a c c u r a t e . The s p o t may be due t o a r e s o r b i n g embryo o r o c c a s i o n a l l y t o a f o l d i n t h e u t e r i n e w a l l . Under f i e l d c o n d i t i o n s i t i s easy t o o v e r l o o k s m a l l s c a r s . C o r p o r a l u t e a a r e v e r y easy t o count when t h e o v a r y i s s e r i a l l y s e c t i o n e d . However, t h e count o b t a i n e d i s g e n e r a l l y somewhat h i g h due t o a c e r t a i n amount of p r e i m p l a n t a t i o n l o s s w h i c h can n o t be t a k e n i n t o a c c o u n t . E u t a m i a s minimus O n l y f o u r p r e g n a n t E_. m. n e g l e c t u s were t a k e n . The number of v i s i b l e embryos was f i v e , f o u r , s i x , and f o u r , a v e r a g i n g 4.75. The l a s t p r e g n a n t f e m a l e t a k e n i n 1968 had two o f the f o u r embryos a p p a r e n t l y r e s o r b i n g as t h e y were i l l formed and much s m a l l e r t h a n t h e o t h e r two embryos p r e s e n t . T h i r t e e n p r e g n a n t E_. m. s c r u t a t o r were t a k e n . The number of embryos c o u n t e d ranged from f i v e t o seven and averaged 5.77. None of t h e embryos c o u n t e d were v i s i b l y b e i n g r e s o r b e d . -35-C o r p o r a l u t e a c o u n t s were made on a l l f e m a l e s c o l l e c t e d . E x c l u d i n g t h o s e w i t h i n c o m p l e t e d a t a , and t h o s e w h i c h can not be a s s i g n e d t o any age c l a s s , t h e f o l l o w i n g r e s u l t s were o b t a i n e d . TABLE I I OVULATION RATES OF LEAST CHIPMUNKS AS INDICATED BY CORPORA LUTEA COUNTS X N s 2 E. m. n e g l e c t u s '67 5.21 24 0.96 E. m. n e g l e c t u s '68 4.38 13 2.09 E. m. s c r u t a t o r *68 4.78 9 2.20 E. m. s c r u t a t o r '69 6.31 16 0.50 X * A t 95% l e v e l X I n d i c a t e s s i g n i f i c a n t d i f f e r e n c e between e s t i m a t e s f o r the two y e a r s . I n no c a s e were c o r p o r a l u t e a found i n an a n i m a l w h i c h was c o n f i r m e d t o be a j u v e n i l e . A l t h o u g h a l l o f t h e 24 c o n f i r m e d a d u l t E. m. n e g l e c t u s f e m a l e s from 1967 had c o r p o r a l u t e a , t h r e e out o f 16 o r 18.7% o f t h e f e m a l e s had no c o r p o r a l u t e a i n 1968. F i v e o u t o f 13 o r 38.5% of t h e _E. m. s c r u t a t o r f e m a l e s had no c o r p o r a l u t e a i n 1968. None o f - t h e 17 p o s t e s t r o u s f e m a l e s t a k e n i n 1969 had f a i l e d t o b r e e d . P l a c e n t a l s c a r s were c o u n t e d i n t h e second y e a r o f s t u d y when t h e y were v i s i b l e i n the u t e r u s . The s c a r s become i m p o s s i b l e t o count u n d e r f i e l d c o n d i t i o n s a f t e r about f i v e weeks p o s t p a r t u m . I n _E. m. n e g l e c t u s , n i n e a n i m a l s had v i s i b l e s c a r s . F i v e o f t h e n i n e c o i n c i d e d e x a c t l y w i t h t h e number o f c o r p o r a l u t e a c o u n t e d . Each o f t h e o t h e r f o u r had one l e s s s c a r t h a n t h e number of c o r p o r a - 3 6 -l u t e a c o u n t e d . The r e m a i n i n g f o u r each had one l e s s p l a c e n t a l s c a r t h a n c o r p o r a l u t e a . T h i s g i v e s a p r e i m p l a n t a t i o n l o s s of f o u r o u t of 87 o r 4 . 6%. Tamias s t r i a t u s O n l y one p r e g n a n t e a s t e r n chipmunk was t a k e n d u r i n g the c o u r s e of t h i s s t u d y . I t had f o u r w e l l d e v e l o p e d embryos. A g a i n e x c l u d i n g a n i m a l s w i t h i n c o m p l e t e d a t a and t h o s e w h i c h can n o t be a s s i g n e d t o a d e f i n i t e age c l a s s , r e s u l t s were o b t a i n e d as i n T a b l e I I I . TABLE I I I OVULATION RATES OF EASTERN CHIPMUNKS AS INDICATED BY CORPORA LUTEA COUNTS X N \ _ S ^ S i g . * T. s_. g r i s e u s ' 67 7 .09 22 5 . 1 3 X T. s_. g r i s e u s ' 6 8 4 . 3 5 37 1.18 * A t 95% l e v e l X I n d i c a t e s s i g n i f i c a n t d i f f e r e n c e between e s t i m a t e s f o r the two y e a r s . O n l y 1 o f 24 o r 4.2% o f the c o n f i r m e d a d u l t e a s t e r n f e m a l e s had no c o r p o r a l u t e a p r e s e n t i n t h e f i r s t y e a r o f s t u d y . Seven o u t o f 43 o r 16.3% of the c o n f i r m e d a d u l t e a s t e r n f e m a l e s had no c o r p o r a l u t e a i n 1 9 6 8 . P l a c e n t a l s c a r s were c o u n t e d i n 23 e a s t e r n chipmunks. F o u r t e e n of t h e 23 c o u n t s c o i n c i d e d e x a c t l y w i t h t h e number o f c o r p o r a l u t e a c o u n t e d . Four o f t h e r e m a i n i n g n i n e c o u n t s were h i g h e r t h a n the number o f c o r p o r a l u t e a c o u n t e d . The c a use of t h i s r e s u l t i s -37-unknown. It could be due to polyovular f o l l i c l e s or some other f a c t o r . Of the remaining f i v e counts, three had one less scar and two had two less scars than the number of corpora lu t e a counted. This gives a preimplantation loss of 6.6%. Timing of Reproduction Eutamias minimus The exact timing and extent of the breeding season i n the le a s t chipmunks were not determined. In both 1967 and 1968, the f i r s t E!. m. neglectus females taken were pregnant and none were taken which were i n estrus. The l a s t pregnant female was taken on May 5, 1967, and on May 24, 1968. Criddle (1934) states that the gestation period i s about 28-30 days. If t h i s were the case, the approximate end of the breeding season occurred wi t h i n a few days of A p r i l 5, 1967, and of A p r i l 24, 1968. Despite the fact that females were no longer i n estrus, males remained i n breeding condition u n t i l May 27, 1967, and May 16, 1968. The e a r l i e s t emergence of young, based on trapping, was June 29, 1967, and July 23, 1968. The l a t t e r date i s probably considerably l a t e r than the actual e a r l i e s t emergence dates. I had d i f f i c u l t y trapping the Minnesota l e a s t chipmunks i n 1968. The f i r s t j u v e n i l e taken i n 1968 was considerably larger than i t s counterpart i n 1967. Emergence of the l e a s t chipmunks from hibernation i n Minnesota i n February would seem highly u n l i k e l y . In both 1967 and 1968, only four days had maximum temperatures of over 32°F. The minimum temperatures were never above 10°F. i n February of 1967 and never - 3 8 -above 20°F. i n F e b r u a r y o f 1968. V a s t f l u c t u a t i o n s i n t e m p e r a t u r e a r e n o t uncommon d u r i n g t h i s month. From a minimum of -34°F. on F e b r u a r y 12, 1967, t h e t e m p e r a t u r e r o s e t o a maximum of 41°F. on F e b r u a r y 13, 1967. A c o n s i d e r a b l e snow c o v e r i n b o t h 1967 and 1968 w o u l d a l s o seem t o m i t i g a t e a g a i n s t a F e b r u a r y emergence. From March 19, 1967, t h e d a i l y maximum t e m p e r a t u r e remained near o r above 32°F. w i t h t h e d a i l y minimums o v e r 20°F. w i t h t h e e x c e p t i o n o f t h r e e d a y s . I n 1968 t h e p a t t e r n was somewhat more ambiguous. A l l b u t s e v e n o f t h e d a i l y maximum t e m p e r a t u r e s were above 32°F. Two p e r i o d s of v e r y low minimum and maximum d a i l y t e m p e r a t u r e s i n t e r v e n e d between p e r i o d s o f g e n e r a l l y m i l d w e a t h e r . From March 13, 1968, w i t h t h e e x c e p t i o n of t h r e e d a y s , t h e maximum d a i l y t e m p e r a t u r e s were n e a r o r above 32°F. A p r i l t e m p e r a t u r e s i n b o t h y e a r s were q u i t e m i l d w i t h t e m p e r a t u r e s i n t h e 40's and 50's common. These weather p a t t e r n s would seem t o l e n d w e i g h t t o a l a t e March and A p r i l b r e e d i n g s e a s o n i n M i n n e s o t a s i n c e b r e e d i n g f o l l o w s emergence from h i b e r n a t i o n v e r y c l o s e l y as I d i s c o v e r e d f r o m t r a p p i n g l e a s t chipmunks i n Oregon. Wadsworth (1969) found t h i s same p a t t e r n i n Eutamias q u a d r i v i t t a t u s i n U t a h . The i n f l u e n c e o f t e m p e r a t u r e on b e g i n n i n g o f b r e e d i n g i n Oregon i s not as r e a d i l y a p p a r e n t . D u r i n g b o t h J a n u a r y and F e b r u a r y o f 1968 and 1969, t h e d a i l y maximum t e m p e r a t u r e s were, w i t h few e x c e p t i o n s , above f r e e z i n g . Snow c o v e r was n o n - e x i s t e n t i n 1968, and a t a v e r y low l e v e l i n 1969. However, minimum d a i l y t e m p e r a t u r e s -39-were u s u a l l y somewhat below f r e e z i n g d u r i n g b o t h months. The d a i l y minimum t e m p e r a t u r e s were comparable t o t h o s e r e c o r d e d f o r M i n n e s o t a j u s t p r i o r t o t h e o n s e t of b r e e d i n g t h e r e . The b r e e d i n g s e a s o n o f IS. m. s c r u t a t o r i n Oregon b e g i n s a l m o s t t h e same t i m e as t h a t c a l c u l a t e d f o r t h e M i n n e s o t a l e a s t chipmunks. M a l e s were c o l l e c t e d f r o m F e b r u a r y 23, 1968, soon a f t e r t h e i r emergence from h i b e r n a t i o n . No sperm was p r e s e n t i n the e p i d i d y m i d e s u n t i l March 4, 1968. Over 40 males were sampled b e f o r e t h e f i r s t f e m a l e s were t a k e n March 26. These f e m a l e s were i n e s t r u s . The f i r s t p r e g n a n t f e m a l e s were t a k e n A p r i l 11. Three o f t h e a n i m a l s t a k e n A p r i l 12 were a l s o i n e s t r u s . I t w o u l d seem l i k e l y t h a t a l l i n s e m i n a t i o n t a k e s p l a c e i n a two t o t h r e e week p e r i o d j u d g i n g f r o m t r a p p i n g r e s u l t s . The e a r l i e s t emergence of t h e young was n o t d e t e r m i n e d . I n 1969, chipmunks were f i r s t t r a p p e d i n Oregon on March 30. Both males and f e m a l e s were t a k e n . The f e m a l e s were a l l i n e s t r u s e x c e p t one w h i c h appeared t o have v e r y r e c e n t l y o v u l a t e d . L o c a l r e s i d e n t s t o l d me of f i r s t s e e i n g chipmunks out on March 8. A t t e m p t s t o t r a p chipmunks on F e b r u a r y 21 and March 5 had been u n s u c c e s s f u l . The f i r s t p r e g n a n t a n i m a l s were t a k e n A p r i l 11. S e v e r a l f e m a l e s were s t i l l a p p a r e n t l y i n e s t r u s a t t h i s t i m e . Females t a k e n A p r i l 30 and May 1 were e i t h e r p r e g n a n t o r l a c t a t i n g . A l l m ales t a k e n i n 1969 were i n r e p r o d u c t i v e c o n d i t i o n . C o l l e c t i v e l y , t h e above i n f o r m a t i o n w o u l d p l a c e t h e t i m i n g o f b r e e d i n g d u r i n g t h e month o f A p r i l . N e i t h e r s u b s p e c i e s o f l e a s t chipmunk was found t o have a second b r e e d i n g s e a s o n . -40-Tamias s t r i a t u s T i m i n g of r e p r o d u c t i o n i n e a s t e r n chipmunks i s a p p a r e n t l y somewhat e a r l i e r t h a n i n t h e l e a s t chipmunks i n M i n n e s o t a . Only one f e m a l e was t a k e n w h i c h was p r e g n a n t . I t was t r a p p e d on A p r i l 18, 1968. A f e m a l e t a k e n May 8, 1967, was a l r e a d y l a c t a t i n g . H a m i l t o n (1943) g i v e s t h e g e s t a t i o n p e r i o d i n t h i s s p e c i e s as 31 d a y s . The main t i m e o f r e p r o d u c t i o n would be l i m i t e d by t h e w e ather i n t h i s s p e c i e s a l s o t o t h e l a t t e r h a l f of March as e x p l a i n e d f o r t h e l e a s t chipmunk. One f e m a l e was t a k e n w h i c h i s t h o u g h t t o have had a second l i t t e r . I t had 12 c o r p o r a l u t e a . Seven o f t h e s e were s i g n i f i c a n t l y s m a l l e r t h a n t h e r e s t , and q u a l i t a t i v e d i f f e r e n c e s were a l s o a p p a r e n t ( F i g . 3 0 ) . The f i v e l a r g e s t c o r p o r a l u t e a had b l o o d c l o t s o f v a r i o u s s i z e s w i t h i n t h e body of t h e c o r p o r a l u t e a . Each of t h e f i v e a l s o were l o c a t e d i n t h e c o r t e x o f t h e o v a r y and r e a c h e d the s u r f a c e somewhere i n t h e i r l e n g t h . The s e v e n s m a l l e r c o r p o r a l u t e a were much more o r g a n i z e d i n c e l l s t r u c t u r e , and t h e y were b e g i n n i n g t o show s i g n s of c o n n e c t i v e t i s s u e i n v a d i n g t h e i r c e n t e r s much as i n t h e l a t e r l a c t a t i n g e a s t e r n f e m a l e s . These s e v e n were a l l l o c a t e d w e l l w i t h i n t h e m e d u l l a r y r e g i o n o f t h e o v a r y and o n l y one r e a c h e d t h e s u r f a c e of t h e o v a r y . The l a r g e r c o r p o r a l u t e a a v e r a g e d about 753 mu. i n g r e a t e s t d i a m e t e r w h i l e t h e s m a l l e r s e v e n c o r p o r a l u t e a a v e r a g e d about 482 mu. i n d i a m t e r . A l l e n (1937) o b s e r v e d t h a t when an e a s t e r n chipmunk l o s e s i t s f i r s t l i t t e r i t c a n e x p e r i e n c e a second e s t r u s and w i l l mate a g a i n . -41-T h i s a n i m a l was l a c t a t i n g when i t was c a p t u r e d J u l y 6 , 1 9 6 7 , w h i l e t h e l a s t f u n c t i o n a l male was t a k e n May 2 8 , 1 9 6 7 . I t seems h i g h l y u n l i k e l y t h a t t h i s f e m a l e c o u l d have s u c c e s s f u l l y r a i s e d i t s f i r s t l i t t e r i n time t o come i n t o e s t r u s a g a i n b e f o r e June 1 . I t s h o u l d be n o t e d t h a t t h e f i r s t j u v e n i l e t r a p p e d i n 1 9 6 7 was t a k e n June 2 3 . P r o b a b l y i s o l a t e d c a s e s such as t h i s l e d Gunderson and Beer ( 1 9 5 3 ) t o c o n c l u d e t h a t Tamias s t r i a t u s may have two b r e e d i n g seasons i n M i n n e s o t a . -42-DISCUSSION Male R e p r o d u c t i v e Organ H i s t o l o g y The h i s t o l o g y and g r o s s morphology o f t h e r e p r o d u c t i v e t r a c t i n b o t h s p e c i e s a r e s i m i l a r i n most major f e a t u r e s t o t h a t of o t h e r s c i u r i d s p e c i e s . However, t h e s y n c h r o n y o b s e r v e d between the f u n c t i o n a l s t a t e s o f t h e t e s t i s and a c c e s s o r y organs i n chipmunks i s somewhat d i f f e r e n t f r o m t h e p a t t e r n o b s e r v e d i n o t h e r s c i u r i d s . McKeever (1966) found t h a t t h e t e s t i s a t r o p h i e d c o n s i d e r a b l y i n advance of t h e a c c e s s o r y organs i n b o t h C i t e l l u s  l a t e r a l i s and C i t e l l u s b e l d i n g i . M i l l a r (1968) found t h e t e s t i s and a c c e s s o r y organs of T a m i a s c i u r i s h u d s o n i c u s i n s y n c h r o n y t h r o u g h t h e f i r s t b r e e d i n g s e a s o n . N e i t h e r t e s t i s nor a c c e s s o r y organs e n l a r g e d p r i o r t o t h e second b r e e d i n g s e a s o n o f t h e y e a r even though a l l t h e organs remained f u l l y f u n c t i o n a l . The s y n c h r o n y of f u n c t i o n a l s t a t e s between t e s t i s and a c c e s s o r y organs o b s e r v e d i n chipmunks may be c o n s i d e r a b l y d i f f e r e n t i n a r e a s where a second b r e e d i n g season i s p r e s e n t . W i t h o u t d a t a on a second b r e e d i n g s e a s o n v a l i d c o m p a r i s o n s between s c i u r i d s a r e v e r y d i f f i c u l t , i f n o t i m p o s s i b l e t o make. An a p p a r e n t s i g n i f i c a n t d i f f e r e n c e between chipmunks and o t h e r s c i u r i d s i s t h e p r e s e n c e of two d i s t i n c t h i s t o l o g i c a l l y d i f f e r e n t a r e a s i n the e p i d i d y m i d e s of b o t h s p e c i e s of chipmunk. The phenomenon has been documented i n s e v e r a l o t h e r mammalian s p e c i e s however. R e i d and C l e l a n d (1957) r e c o g n i z e 11 zones and subzon.es i n t h e e p i d i d y m i s of t h e r a t . N i c a n d e r (1957, 1958) - 4 3 -d i s t i n g u i s h e s e i g h t r e g i o n s i n t h e r a b b i t and s i x r e g i o n s i n the s t a l l i o n , ram, and b u l l . W i s l o c k i ( 1 9 4 9 ) o b s e r v e d two d i s t i n c t r e g i o n s i n t h e deer e p i d i d y m i s w i t h t a l l e r e p i t h e l i a l c e l l s i n t h e p r o x i m a l p o r t i o n o f t h e e p i d i d y m i s and l o w e r c e l l s i n t h e d i s t a l p o r t i o n . T h i s a p p e ars t o p a r a l l e l t h e s i t u a t i o n i n the chipmunk q u i t e c l o s e l y . C l e l a n d and Rae (1963) d e f i n e 16 zones and subzones i n t h e b a n d i c o o t e p i d i d y m i s . These c l a s s i f i c a t i o n s o f zones and subzones a r e based on some c o m b i n a t i o n o f l u m i n a d i a m e t e r s , e p i t h e l i a l h e i g h t s , l o c a t i o n of t h e n u c l e u s , l o c a t i o n of the G o l g i b o d i e s , c y t o c h e m i c a l v a r i a t i o n s , and p r e s e n c e o r absence of s t e r e o c i l i a . E a r l i e r i n v e s t i g a t o r s n o t i c e d d i f f e r e n c e s i n a r e a s of t h e e p i d i d y m i d e s of t h e dog, h a r e s , m i c e , and g u i n e a p i g s ( v i s N i c a n d e r , 1 9 5 7 ) . More r e c e n t l y B a r r o n and McEnery (1966) r e a f f i r m e d t h a t such d i f f e r e n c e s e x i s t i n t h e mouse, and Hanoman and McEnery (1967) l a t e r found t h a t t h e s e c h a r a c t e r s a r e t r a c e a b l e from b i r t h . M a r f a n and R i s e l y (1963) have shown t h a t changes i n h e i g h t of the e p i t h e l i u m and l u m i n a d i a m e t e r s change w i t h s e x u a l a c t i v i t y . Such a f i n d i n g would seem t c i n d i c a t e t h a t r e c o g n i t i o n of 11-16 zones on the b a s i s o f r e s u l t s from a few r e . p r o d u c t i v e l y a c t i v e a n i m a l s c o u l d be somewhat m i s l e a d i n g . The e p i d i d y m i d e s o f t h e chipmunk a l s o undergo change i n h e i g h t h o f the e p i t h e l i u m and l u m i n a d i a m e t e r s d u r i n g t h e c o u r s e of the r e p r o d u c t i v e c y c l e . No d i s t i n c t i o n c o u l d be made between a r e a s e x c e p t i n a n i m a l s i n f u l l b r e e d i n g c o n d i t i o n . I n t h e c h i p -munk t h e change from one t u b u l a r t y p e t c a n o t h e r o c c u r s i n a -44-r a t h e r l i m i t e d a r e a and q u i t e a b r u p t l y u n l i k e t h e g r a d u a l i n t e r g r a d a t i c n of c e l l t y p e s d e s c r i b e d f o r s e v e r a l of t h e o t h e r s p e c i e s . Perhaps t h i s w o u l d n o t be t h e c a s e i f more zones were d e f i n e d u s i n g d i f f e r e n t h i s t o c h e m i c a l t e c h n i q u e s t o emphasize c e r t a i n c e l l o r g a n e l l e s . The r e l a t i o n s h i p between s t r u c t u r e and f u n c t i o n i n t h e e p i d i d y m i s r e m a i n s t o be d e t e r m i n e d . B o t h s e c r e t o r y and r e s o r p t i v e f u n c t i o n s would appear r e a s o n a b l e g i v e n the d r a m a t i c d i f f e r e n c e s i n c e l l t y p e s w h i c h I found i n t h e chipmunk e p i d i d y m i s . These two f u n c t i o n s f o r t h e e p i d i d y m i s a r e most w i d e l y p r o p o s e d by o t h e r w o r k e r s i n v e s t i g a t i n g t h e e p i d i d y m i s . A l t h o u g h t h i s c h a r a c t e r i s t i c has been d e s c r i b e d i n o n l y t h r e e a n i m a l s o t h e r t h a n d o m e s t i c s t o c k , i t s p r e s e n c e i n o t h e r mammals remains a good p o s s i b i l i t y . Such a c h a r a c t e r c o u l d e a s i l y be. o v e r l o o k e d s i n c e i t o c c u r s p r o m i n e n t l y o r e x c l u s i v e l y i n r e p r o d u c t i v e l y a c t i v e a n i m a l s . A l s o t h e d i f f e r e n t t u b u l e t y p e s a r e p r e s e n t t o g e t h e r i n l e s s than 1/3 of t h e l e n g t h of t h e e p i d i d y m i d e s i n t h e chipmunk ana c o u l d p o s s i b l y be m i s s e d d u r i n g s e c t i o n i n g . A c l e a r u n d e r s t a n d i n g c f the f u n c t i o n of t h e d i f f e r e n t t u b u l e t y p e s w o u l d u n d o u b t e d l y c l e a r up much of t h e c o n f u s i o n and c o n t r o v e r s y o v e r t h e o v e r a l l f u n c t i o n of t h e e p i d i d y m i s . Female R e p r o d u c t i v e Organ H i s t o l o g y The f e m a l e chipmunks a l s o show t h e n o r m a l p a t t e r n d e s c r i b e d i n o t h e r s c i u r i d s . C o r p o r a l u t e a a r e m a i n t a i n e d i n the o v a r i e s t h r o u g h o u t l a c t a t i o n w i t h l i t t l e d e c r e a s e i n s i z e . T h i s c o r r e s p o n d s -45-to the s i t ua t ion described for Marmota monax (Rasmussen, 1918), C i t e l l u s tridecemlineatus (Drips, 1919), C_. l a t e r a l i s and C_. be ld ing i (McKeever, 1966) but not for Sciurus carol inensis (Deans!}' and Parkes, 1933). The corpora lutea remain evident w e l l in to the f a l l since animals taken as la te as August 31, i n the case of E_. minimus, and as la te as October 2, i n the case of T_. s t r i a t u s , s t i l l had v i s i b l e corpora lu tea . In no animals did I f ind evidence of corpora lutea from the previous year. Age at. Maturi ty A l l evidence for both species i n this: study suggests that juveni les do not become sexually act ive u n t i l the spring fol lowing the i r b i r t h . This i s not surpr i s ing i n view of the fact there was no summer breeding season observed i n ei ther year of the study. By the end of summer the. ovaries of juveni le chipmunks begin tc show quite advanced f o l l i c l e s . These are comparable to those found i n mature females at the same time. The males however show nc signs of maturation i n the f a l l . There i s no apparent increase i n seminiferous tubule diameter nor any ind ica t ion of a c t i v i t y i n the accessory organs. The s ize of a l l reproductive organs i n the male are s t i l l somewhat smaller than these of the non-functional adult male at the same time. Eutamias minimus and Tamias s t r i a tus The s i m i l a r i t i e s between the two species of chipmunks are far mere prevalent than are the differences. The most read i ly apparent -46-d i f f e r e n c e i s one o f s i z e . A l l r e p r o d u c t i v e organs o f b o t h sexes a r e a p p r o x i m a t e l y 1.5-2.0 t i m e s as l a r g e i n t h e e a s t e r n chipmunk as i n t h e l e a s t . However, t h e e x t e r n a l s i z e d i f f e r e n c e does n o t h o l d t r u e h i s t o l o g i c a l l y . A l m o s t a l l t u b u l e d i a m e t e r s , c o r p o r a l u t e a d i a m e t e r s , and e p i t h e l i a l h e i g h t s were o f much t h e same ma g n i t u d e . The h i s t o l o g i c a l p i c t u r e , as had been p o i n t e d out e a r l i e r i n t h e p a p e r , i s v i r t u a l l y i d e n t i c a l i n each s p e c i e s . The t i m i n g o f r e p r o d u c t i o n i s the o n l y m a j o r d i f f e r e n c e w i t h t h e e a s t e r n chipmunk a p p a r e n t l y b e i n g about two weeks e a r l i e r i n each phase j u d g i n g from p r e g n a n t a n i m a l s c a u g h t . T h i s r e s u l t s i n an e a r l i e r emergence d a t e f o r t h e young o f t h e e a s t e r n c h i p -munk t h a n f o r t h o s e o f the l e a s t ( F o r b e s , 1966). T i m i n g o f R e p r o d u c t i o n The t i m i n g o f r e p r o d u c t i o n as d e t e r m i n e d i n t h i s s t u d y a g r e e s c l o s e l y w i t h t h a t f o u n d a t s i m i l a r l a t i t u d e s by o t h e r i n v e s t i g a t o r s . I n f o r m a t i o n on t h e e a s t e r n chipmunk i s a v a i l a b l e f o r d i f f e r e n t a r e a s by s e v e r a l a u t h o r s . A l l e n (1938) and Y e r g e r (1955) found t h a t t h e b r e e d i n g s e a s o n e x t e n d s from about March 17 t o A p r i l 7 i n c e n t r a l New Y o r k . B o t h found e v i d e n c e o f a second b r e e d i n g s e a s o n w i t h t h e second l i t t e r b e i n g b o r n l a t e i n J u l y o r e a r l y i n A u g u s t . M a n v i l l e (1949) s u g g e s t s t h a t b r e e d i n g b e g i n s i n A p r i l i n n o r t h e r n M i c h i g a n . He a l s o found e v i d e n c e o f a second l i t t e r b e i n g b o r n i n l a t e r J u l y o r e a r l y A u g u s t . S c h o o l e y (1934) p l a c e s the b e g i n n i n g o f b r e e d i n g a t t h e f i r s t week i n A p r i l i n I n d i a n a . He -47-a l s o s t a t e s a second b r e e d i n g s e a s o n o c c u r s , b u t he s u g g e s t s the f e m a l e s w h i c h a r e b r e d a r e m o s t l y young o f the y e a r and o l d e r f e m a l e s w h i c h f a i l e d t o b r e e d i n t h e s p r i n g s e a s o n . T h i s second s e a s o n o c c u r s i n J u l y . B u r t (1940) i n s o u t h e r n M i c h i g a n p l a c e s the o n s e t o f b r e e d i n g a t about A p r i l 1 w i t h t he second s e a s o n b e g i n n i n g i n l a t e J u l y o r A u g u s t . O t h e r s who g i v e e v i d e n c e o f two b r e e d i n g seasons f o r the e a s t e r n chipmunk a r e B l a i r (1942), Gunderson and Beer (1953), Panuska and Wade (1957) , and J a c k s o n (1961). F o r b e s (1966) w o r k i n g i n n o r t h e r n M i n n e s o t a found no e v i d e n c e o f a second b r e e d i n g season i n two summers o f work. One p r e g n a n t f e m a l e was t a k e n i n l a t e June. T h i s c o u l d w e l l have been a n o t h e r example o f a fe m a l e l o s i n g h e r f i r s t l i t t e r and b r e e d i n g a second t i m e . M a n v i l l e (1949) g i v e s e v i d e n c e o f two p o s s i b l e b r e e d i n g seasons f o r t h e l e a s t chipmunk i n n o r t h e r n M i c h i g a n . B r e e d i n g o c c u r s i n t h i s s p e c i e s i n e a r l y A p r i l as w e l l . C r i d d l e (1943) found no e v i d e n c e of a second b r e e d i n g s e a s o n i n n a t u r e i n s o u t h e r n M a n i t o b a . However, i f t h e young o f a f e m a l e k e p t i n c a p t i v i t y were k i l l e d e a r l y i n the l a c t a t i o n p e r i o d , t h e f e m a l e would b r e e d a g a i n b r i n g i n g o f f t h e second l i t t e r i n l a t e June. C r i d d l e t o o k f o r t y - o n e p r e g n a n t f e m a l e s from A p r i l 25 t o May 25. The main b r e e d i n g s e a s o n b e g i n s i n A p r i l . F o r b e s (1966) found no e v i d e n c e o f a second b r e e d i n g s e a s o n i n t h i s s p e c i e s i n n o r t h e r n M i n n e s o t a e i t h e r . From t h i s i n f o r m a t i o n t h e r e a p p e a r s t o be a band 200-300 m i l e s wide i n w h i c h b r e e d i n g b e g i n s i n A p r i l w i t h s l i g h t l y e a r l i e r o n s e t o f b r e e d i n g i n chipmunks s l i g h t l y f u r t h e r s o u t h . I f i n f o r m a t i o n on t h e o n s e t o f b r e e d i n g and p r e s e n c e o r absence o f a second b r e e d i n g -4g-season were ava i lab le from Georgia, South Caro l ina , or other southern extremes of the range of the eastern chipmunk i t may be possible to assign the lack of a second breeding season on the r e l a t i v e l y short period of a c t i v i t y further north. No information i s avai lable concerning the breeding biology of the least chipmunk i n Alaska or the northern portions of the western provinces for comparison with the s i tua t ion i n Minnesota. Fecundity The s t a t i s t i c a l l y s ign i f i can t difference found i n ovulat ion rates for each chipmunk between the two years of the study are very i n t e r e s t i ng . Lowered ovulat ion ra tes , higher preimplantation l o s s , and higher percentage of females which f a i l e d to breed en t i r e ly appear to be working i n concert to lower the fecundity the second year of the study i n Minnesota. The f i r s t summer of the study both chipmunks had r e l a t i v e l y high ovulat ion rates and only one of the 45 females taken had f a i l e d to ovulate. The second year the ovulat ion rate dropped i n both species. At the same time the number of females which f a i l e d to ovulate rose to 10 out of 49 or almost 1/5 of the females taken. The second year also 10 out of 32 or almost 1/3 of the females had preimplantation losses as indicated by placenta l scar counts. I t seem apparent that some external factor was affect ing the fecundity of the Minnesota ch ip-munks since both were affected i n the same manner. No apparent s ign i f i can t change i n weather patterns p r io r to entering hibernation i n the f a l l , increase or decrease i n snow cover over winter and - 4 9 -e a r l y s p r i n g , m a r k e d l y d i f f e r e n t c o n d i t i o n s upon emergence from h i b e r n a t i o n , n o r change i n amount o f r a i n f a l l t h r o u g h t h e summer can be s u g g e s t e d as r e a s o n s f o r t h e change i n f e c u n d i t y o b s e r v e d . The Oregon chipmunks a l s o show a s i g n i f i c a n t change i n t h e o v u l a t i o n r a t e . A g a i n f a i l u r e t o o v u l a t e and l o w e r e d o v u l a t i o n r a t e s c o i n c i d e d . The second y e a r when o v u l a t i o n r a t e s were h i g h none o f t h e 17 p o s t e s t r o u s chipmunks t a k e n had f a i l e d t o o v u l a t e . T hree o f t h e 17 had e x p e r i e n c e d p r e i m p l a n t a t i o n l o s s e s . The f i r s t y e a r when o v u l a t i o n r a t e s were low a v e r y h i g h p r o p o r t i o n o f t h e f e m a l e s f a i l e d t o b r e e d e n t i r e l y . I t i s i n t e r e s t i n g t o n o t e t h a t the y e a r of v e r y low r e p r o d u c t i o n c o i n c i d e d i n the M i n n e s o t a and Oregon chipmunk p o p u l a t i o n s . -50-CONCLUSIONS The general h is tology of the reproductive organs i n the chipmunk i s very s i m i l a r to that described for other s c i u r i d s . The one major aspect heretofor undescribed i s the presence of d i s t i n c t i v e regions i n the epididymides during periods of act ive sperm production. Regional va r i a t i on occurs i n some non-sciur id mammals, but the difference i s not as dramatic nor i s the change from one tubule type to another as abrupt as that found i n the chipmunk. This opens up an excel lent research vehic le for further e luc ida t ion on the function or functions of the epididymis. The onset of reproduction occurs very soon after emergence from hibernation wi th the males coming out somewhat e a r l i e r than the females. The breeding a c t i v i t i e s are completed w i th in two weeks to a month with most males remaining i n condition throughout the per iod. Through the use of a computer program for aging the animals, I established a r e l i a b l e device for d is t inguishing between juveni le and adult females. The program uses t r a d i t i o n a l aging parameters, but removes the subjective nature of the decision on the r e l a t i v e age of any i n d i v i d u a l animal. The actual fecundity of a population i s then more accurately determined; since juveni les which were never i n reproductive condit ion are excluded from estimates of the fecundity. Neither juveni le males or females contribute to the breeding population u n t i l the spring fol lowing thei r b i r t h . The more accurate determination of fecundity i n turn makes -51-the v a r i a t i o n observed between the two summers more revealing. The p a r a l l e l nature of change observed i n both the eastern and le a s t chipmunk suggests that there may be a common environmental f a c t o r inducing s h i f t s i n fecundity l e v e l s . These differences i n fecundity are brought about by a combination of changes i n ovulation rates, preimplantation l o s s , and resorption of embryos. PLATE 1 - The Test is and Epididymis F i g . 1. Juvenile Test is - 125 X - (T. s t r i a tus ) - Closely packed seminiferous tubules of small diameter, closed lumina, and very l i t t l e i n t e r s t i t i a l t issue characterize th is stage. F i g . 2. Functional Test is - 105 X - (E. minimus) - The seminiferous tubules are greatly enlarged, with sperm evident i n the open lumina. I n t e r s t i t i a l t issue i s more evident than i n the j uven i l e . F i g . 3. Non-Functional Adult: Testis - 96 X - (E. minimus) Seminiferous tubules appear almost i d e n t i c a l to those i n the juveni le except for a s l i g h t l y greater diameter. F i g . 4. Juvenile Epididymis - 110 X - (E. minimus) - No sperm are present i n the epididymis and the epithelium i n the tubules i s cuboidal i n a l l areas. F i g . 5. Functional Epididymis - 54 X - (E_. minimus) - The tubules with cuboidal epithelium (a) are part of the vasa e f fe ren t ia . The tubules l i ned with t a l l columnar epithelium which has centra l n u c l e i , and no sperm i n the lumina (b) , are part of the r e s t r i c t ed f i r s t por t ion of the epididymis. The tubules l i ned with columnar epithelium which has basal nuc le i and sperm f i l l e d lumina (c) are found throughout most of the length of the epididymis. F i g . 6. Non-Functional Adult Epididymis - 100 X - (E. minimus) The reversion to juveni le appearance with low e p i t h e l i a l heights , open lumina, and no apparent differences between the two areas of the epididymis are always found i n th i s stage. PLATE 2 - The Seminal V e s i c l e s F i g . 7. Rete T e s t i s - Vasa E f f e r e n t i a Junction - 127 X -(E_. minimus) - The area of fusion occurs over a li m i t e d region. F i g . 8. Juvenile Seminal Vesicles - 264 X - (T. s t r i a t u s ) -The epithelium i s cuboidal with no secretion evident. F i g . 9. Functional Seminal Vesicles - 264 X - (T. s t r i a t u s ) -The lumina are completely clogged with highly e o s i n o p h i l i c secretion. The epithelium i s low columnar. F i g . 10. Late Functional Seminal V e s i c l e - 256 X - (E. minimus) -The sec r e t i o n takes on a granular appearance and i s completely absent from some lumina at t h i s stage. The epithelium i s s t i l l columnar. F i g . 11. Non-Functional Adult Seminal V e s i c l e - 303 X -(J_. s t r i a t u s ) - A ju v e n i l e appearance with cuboidal epithelium and empty lumina i s evident at this stage. PLATE 3 - The Prostate and Cowper's Gland F i g . 12. Juvenile Prostate - 248 X - (T. s t r i a tus ) - There i s no evidence of secretion i n the nests of c e l l s present. F i g . 13. Functional Prostate - 131 X - (E. minimus) - Open lumina bordered by low columnar secretory epithelium characterize th i s stage. F i g . 14. Non-Functional Adult Prostate - 248 X - (T. s t r i a tus ) -The lumina close and the epithelium becomes more heavi ly nucleated and appears quite s i m i l a r to the juveni le prostate. F i g . 15. Juvenile Cowper's Gland - 256 X - (E. minimus) -Empty lumina and cuboidal epithelium are apparent. F i g . 16. Functional Cowper's Gland - 256 X - (E. minimus) -The epithelium becomes columnar and the lumina i s clogged wi th eos inophi l i c secret ion. The secret ion hardens i n the f i xa t i ve and normally fractures badly during sect ioning. F i g . 17. Non-Functional Cowper's Gland - 248 X - (T. s t r i a tus ) -Reversion to juveni le state i s cha rac te r i s t i c of this accessory, organ a l so . PLATE 4 - The Ovary F i g . 18. Juvenile Ovary - 131. X - (E. minimus) - Naked ova i n the cortex and abundant primary f o l l i c l e s are t y p i c a l at th i s stage. F i g . 19. Estrous Ovary - 127 X - (E_. minimus) -Corpora lutea are absent i n th is stage. A s ingle large developing f o l l i c l e can be seen i n the upper r ight hand corner of the photograph. F i g . 20. Ovary of Pregnancy - 102 X - (E. minimus)- The only animals taken i n which a small blood c lo t was present i n the corpora lutea had l i t t l e or no detectable swel l ing i n the uterus. F i g . 21. Ovary of Lactat ion - 92 X - (E. minimus) - Corpora lutea i n the leas t chipmunk never have densely s ta in ing connective t issue areas wi th in them. Compare the corpus luteum of the least chipmunk with that of the eastern chipmunk i n F i g . 22. F i g . 22. Ovary of Lacta t ion - 83 X - (T. s t r i a tus ) - The connective t issue region i s apparent w i th in the corpora lutea of the eastern chipmunk u n t i l at least September. F i g . 23. Anestrous Ovary - 96 X - (T. s t r i a tus ) - The corpora lutea are considerably reduced i n s i z e , but s t i l l v i s i b l e even i n la te August as i s the case i n this female. -55-PLATE 5 - The Uterus and Vagina F i g . 24. Juvenile Uterus - 121 X - (E. minimus) - Three concentric bands of t i s sue , the endometrium, myometrium, and advential layer are evident i n this photograph. None of these layers are very th ick or complex at th is stage. F i g . 25. Estrous Uterus - 240 X - (E. minimus) - The endometrium becomes columnar and both the number and complexity of endometrial glands seem to increase. J F i g . 26. Uterus of Lacta t ion - 264 X - (T. s t r i a tus ) - The endometrium returns to a cuboidal or very low columnar height and the number of endometrial glands seem to decrease. F i g . 27. Juvenile Vagina - 120 X - (E. minimus) - Concentric bands of t issue are evident i n th is photograph. The width of these layers increases tremendously i n the estrous animal. F i g . 28. Estrous Vagina - 300 X - (E. minimus) - A thick s t r a t i f i e d , corn i f ied epithelium as w e l l as a mass of debris i n the lumen are indica tors of estrous i n the chipmunk. F i g . 29. Anestrous Vagina - 240 X - (T. s t r i a tus ) - The epithelium charac te r i s t ics i n th i s group are indis t inguishable from the condit ion of the vagina i n ei ther pregnant or l ac ta t ing females. Other than a s l i g h t increase i n o v e r a l l s i ze of the vagina, th i s stage also c lose ly resembles the juveni l i PLATE 6 - Special Ovary of Eastern Chipmunk F i g . 30. Ovary of Female With a Second L i t t e r - 125 X -(T_. s t r i a tus ) - The presence of both corpora lutea with a def in i te connective t issue center and corpora lutea with large blood c lo ts suggests that this female has ovulated on two occasions. - 5 7 --58-ACKNOWLEDGEMENTS I wish to thank my supervisor, Dr. J . M. Taylor, whose advice, encouragement, and assistance were always f r e e l y given. Dr. N. R. L i l e y , Dr. H. D. F i s h e r , and Dr. 1 McT. Cowan provided h e l p f u l c r i t i c i s m and advice. Discussions with fellow graduate students, Mr. John M i l l a r i n p a r t i c u l a r , were u s e f u l at many times during the study. I am g r a t e f u l to a l l of £hese people and many others for help throughout the course of the study. F i n a l l y , I wish to e s p e c i a l l y thank my wife, Jean, f o r her patience and encouragement. Without her help, the study would not have been completed. -59-REFERENCES Allen, E.G. 1938. The habits and l i f e history of the eastern chipmunk, Tamias striatus l y s t e r i . N . Y . State Mus. Bull. 314. 122p. Barron, J. and W. McEnery 1966. Serial histology of the epididymis of the mouse. Anat. Rec. 154:449 Blair, W.F. 1942. Size of the home range and notes on the l i f e history of the woodland deer mouse and eastern chipmunk i n northern Michigan. J. Mammal. 23:27-36. Burt, W.H. 1940. T e r r i t o r i a l behaviour and population of some small mammals in southern Michigan. Univ. Mich, Misc. Publ. Zool., No. 4 5 : 1-58. Cleland, K.W. and CA. Rae 1963. DNA content and volume of bandicoot epididymal duct nuclei. J. Anat. 97:492. Condrin, J.M. 1936. Observations on the seasonal and reproductive a c t i v i t i e s of the eastern chipmunk. J. Mammal. 17:231-234. Criddle, S. 1943. The l i t t l e northern chipmunk in southern Manitoba. Canadian Field-Nat. 57:81-86. Deansly, R. and A.S. Parkes. 1933. The reproductive processes of certain mammals. Part IV. The oestrus cycle of the gray squirrel (Sciurus carolinensis). P h i l . Trans. R. Soc. B. 222:47-78. Dixon, W.J., ed 1964. BMD: Biomedical Computer Programs. UCLA Press, Los Angeles. 585p. Drips, D. 1919. Studies on the ovary of the spermophile (Spermophilus c i t e l l u s tridecemlineatus) with special reference to the corporus luteum. Am. J. Anat. 25:117-184. Forbes, R.B. 1966. Studies of the biology of the Minnesota chipmunks. Amer. Mid. Nat. 76:290-308. -60-F o s t e r , M. A. 1934. The r e p r o d u c t i v e c y c l e i n the female ground s q u i r r e l , C i t e l l u s t r i d e c e m l i n e a t u s ( M i t c h i l l ) Am. J . Anat. 54:487-511. Gunderson, H. L. and J . R. Beer 1953. The Mammals o f M i n n e s o t a . U n i v . M i n n . P r e s s , M i n n e a p o l i s . 190 p. H a m i l t o n , W. J . J r . 1943. The Mammals of the E a s t e r n U n i t e d S t a t e s . Comstock P u b l i s h i n g Co., I n c . I t a c a , N. Y. 432 p. Hanoman, H. and W. McEnery 1967. 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R e p r o d u c t i o n i n C i t e l l u s b e l d i n g i and C i t e l l u s l a t e r a l i s i n n o r t h e a s t e r n C a l i f o r n i a . I n Co m p a r a t i v e B i o l o g y o f R e p r o d u c t i o n i n Mammals, ( I . W. Rowlands, e d . ) . Academic P r e s s I n c . , N. Y. 559 p. M i l l a r , J . S. 1968. The R e p r o d u c t i v e B i o l o g y o f t h e Wes t e r n Red S q u i r r e l . Ms.c. T h e s i s . U n i v . o f B.C. 86 p. Moore, C. R., G. F. Simmons, L. J , W e l l s , M. Z a l e s k y , and W. A. N e l s o n 1934. On C o n t r o l o f r e p r o d u c t i v e a c t i v i t y i n an a n n u a l - b r e e d i n g mammal ( C i t e l l u s t r i d e c e m l i n e a t u s ) . Anat. Rec. 60:279-289. -61-Mossman, H. W. 1966. The Rodent Ovary. In Comparative Biology of Reproduction i n Mammals, (I. W. Rowlands, ed.). Academic Press Inc., New York. 559 p. Mossman, H. W., R. A. Hoffman, and C. M. Ki r k p a t r i c k . 1955. The accessory g e n i t a l glands of male gray and fox s q u i r r e l s correlated with age and reproductive cycles. Am. J . Anat. 97:257-302. Mossman, H. W., J . W. Lawlah, and J . A. Bradley 1932. The male repro-ductive t r a c t of the Sciuridae. Am. J . Anat. 51:89-155. Neff, W. H. and A. Anthony 1963. Seasonal changes i n the male repro-ductive t r a c t of the eastern chipmunk, Tamias s t r i a t u s . Proc. of the Penn. Acad, of Sciences 37:64-70. Nicander, L. 1957. On the regional histology and cytochemistry of ductus epididymis i n r a b b i t s . Acta. Morphol. Neerl-Scan. 1:99-118. Nicander, L. 1958. Studies of the regional histology and cytochemistry i n s t a l l i o n s , rams and b u l l s . Acta. Morphol. Neerl-Scan. 1:337-362. Panuska, J . A. and N. J . Wade 1957. F i e l d observations on Tamias  s t r i a t u s . J . Mammal. 38:192-196. Rasmussen, A. T. 1918. C y c l i c changes i n the, i n t e r s t i t i a l c e l l s of the ovary and t e s t i s i n the woodchuck Marmota monax. Endocrin. 2:353-404. Reid, B. L. and K. W. Cleland 1957. The structure and function of the epididymis. I. The histology of the rat epididymis. Aust. J . Zool. 5:223-246. Schooley, J . P. 1934. A summer breeding season i n the eastern chipmunk, Tamias s t r i a t u s . J . Mammal. 15:194-196. -62-Wadsworth, C. E. 1969. Reproduction and Growth of Eutamias quadrivi t ta tus i n southeastern Utah. J . Mammal. 50:256-261. W i s l o c k i , G. 1949. Seasonal changes i n the tes tes , epididymides and seminal ves ic l e s of deer investigated by histochemical methods. Endoc. 44:167-189. Yerger, R. W. 1955. L i f e h i s tory notes on the eastern chipmunk, Tamias  s t r i a tus l y s t e r i (Richardson), i n New York. Amer. Mid . Nat. 53:312-323. 

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