344 



COMPARATIVE MORPHOLOGY OF VERTEBRATES. 



when the two are inserted in the cloaca the grooves unite to form a 

 tube for the passage of the sperm. There is a large gland in the 

 clasper but its relation to copulation and fertilization is unknown. 



In the snakes and lizards a second kind of structures occurs. In 

 the young there are developed behind the vent a pair of sacs presenting 

 the appearance of appendages. With farther growth these two 

 hemipenes are withdrawn into a sac opening into the hinder side of 



FIG. 343. Cloacal region of adult turtle (Emys lutaria), after von Moller. The 

 rectum and cloaca have been laid open from the dorsal surface and the urogenital sinus 

 exposed. From the opening of the sinus into the cloaca a seminal groove extends along 

 the ventral cloacal surface and can be cut off by a pair of folds (plica urorectales) from the 

 cloacal cavity, av, anal vesicle; b, urinary bladder; o, opening of anal vesicle into cloaca; 

 p, penis, exserted; pu, plicae urorectales; r, rectum; sg, seminal groove; ug, urogenital 

 groove. 



the cloaca. Each hemipenis bears a spiral groove for the passage of 

 the sperm. At the time of copulation these are everted through the 

 anus (fig. 342). 



In all other aminotes the copulatory organs are formed from the 

 same anlage. The lower anterior wall of the cloaca is largely con- 

 cerned in this, the anterior cloacal lip being produced into a genital 

 prominence (fig. 336) which can be traced in many forms as the 

 clitoris of the female and the glans penis of the male. In the embryos 

 of the higher mammals it is surrounded by a pair of integumental 



