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hemipenes are withdrawn into a sac opening into the hinder side of 
Fic. 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 (plice urorectales) from the 
cloacal cavity. av, anal vesicle; 6, urinary bladder; 0, opening of anal vesicle into cloaca; 
p, penis, exserted; pu, plice urorectales; 7, 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 
