316 



PHYSIOLOGY OF GONADS 



ent species, in which breeding is at its 

 height. Sperm cells are formed only during 

 this period. The accessory sex structures are 

 under intense androgenic stimulation. After 

 the breeding season, regression occurs. For 

 the remainder of the year spermatogenesis 

 does not take place and the state of the 

 accessory system resembles that of a cas- 

 trated animal (Fig. 5.4). 



The second type is the continuous 



breeder. Rat, mouse, guinea pig, rabbit 

 (under laboratory conditions) , and man are 

 well known examples. In this type, the 

 testes and accessory sex structures main- 

 tain a constant state of activity, and breed- 

 ing can occur at any time of the year. 



The ram is an intermediate type of 

 breeder, in which spermatogenesis is ar- 

 rested in the nonbreeding season with a 

 concomitant decrease in number of Leydig 



LATERAL FAT 



eONVOLUTgO DU 



j^' 



COWPtR'S 



a 



\\ 



y 



^S^M^ifS) 



EPIDIDYMIS 



VAS DEFERENS 

 CONVOLUTED DUCT 

 PROSTATE 

 SEMINAL VESICLE 

 URETHRA 



COWPER'S OLANO 

 BULBAR OLANO 



Fig. 5.4. Reproductive tract of a seasonal hrrrdrr, the prairie dog, Cynumys. a. Anatomy 

 of male reproductive tract and its abdoiinii.il i( l.ilionships during period of sexual activity. 

 b. Diagrammatic representation of the PCNu.illy adive and the involuted reproductive tracts 

 (dorsal view). (From A. Anthony. J. Morpliol., 93, 331, 1953.) 



