MAMMALIA 



307 



thus producing usually a median part of the uterus and also 

 the vagina. 



In the meantime the Wolman duct and the ureter have 

 been separated, the ureter remaining connected with that 

 part of the cloaca which contributes with the upper end of 

 the allantois to form the bladder. The Wolman duct and the 

 Miillerian duct at their posterior ends open into the cloaca. 



According to sex, the after- development is accompanied 

 by a degeneration, in the case of the male, of the Miillerian 

 duct, and in the case of the female of the Wolman duct. The 



Mesoneph. Metaneph. Ureter Rectum 



Wolffian or mesonepk. duct Att. Cloaca Proct. 'Postanal gut 



Matter, duct 



FIG. 144. The embryonic condition of the ducts at the posterior end 

 of the body. 



terminal end of the intestine is shut out from the cloaca, 

 which is thus resolved into the anus and the urinogenital 

 canal. 



At first the urinogenital canal is similar in both sexes, 

 but, as development proceeds, folds appear on each side of 

 the opening. These form the vulva of the female, and fuse 

 in the male to form the scrotal sacs, and the canal in the male 

 is further produced by the development of the penis. The 

 penis is also formed on the anterior side of the vulva of the 

 female as the clitoris, but remains small. 



It will not be difficult with this explanation to understand 

 the conditions which may be followed in a dissection of the 

 rabbit. The kidneys are situated one on each side of the 

 abdomen. They are covered by the peritoneum. Each has the 

 typical kidney shape. Sections show that they are made up 



