UROGENITAL ORGANS 



367 



Sphenodon lacks copulatory organs, but they occur in all other sauropsida, 

 though formed on two entirely different plans, one restricted to the squamata, 

 the other, occurring in the crocodiles, turtles and some birds, being homologous 

 with those of the mammalia. 



In the young squamata (snakes and 

 lizards) a couple of sacs are developed 

 from the posterior wall of the transverse 

 anus, and in the embryonic stages they 

 resemble appendages. These form the 

 copulatory organs which are called hemi- 

 penes. (These are present in both sexes, 



A 



iv^ 



Tig. 388. Fig. 389. 



Fig. 388. — A, genitalia of hen; B, cloacal region of cock, after Tichomiroff. a, 

 albumen secreting region of oviduct;/, discharged follicle of ovary; 0, advanced ova in 

 follicles; ot, ostium tubse abdominale; r, rectum; s, openings of vasa deferentia; u, 

 urinary openings; «<, uterus or shell gland with the villi showing in the opening. 



Fig. 389. — Hemipcnes of Crotalus horridus, after J. Mliller. One hemipenii U 

 exserted, the other retracted but laid open, cl, cloaca; g, seminal groove; p, hemipenii; 

 r, rectum, rp, retractor muscle of hemipems; u, ureter; vd, vas deferens (Wolffian duct). 



though much smaller in the female.) With further growth these develop re- 

 tractor muscles and are drawn back into pockets (fig. 389). Each hemipenis, 

 which may be notched or bifid at the tip, has a somewhat spiral groove on the 

 medial surface for the passage of the spermatozoa. These hemipenes are 

 everted for copulation and are retracted at other times. 



In the other sauropsida there is a single penis, developed from the same 



