UROGENITAL SYSTEM 



bladder can be formed either in each separate ureter, or at 

 their point of union, or at a still lower point. The Amphibians 

 retain only the posterior part of the Wolffian bodies in a 

 perfect state, either as a coherent mass or in the form of con- 

 secutive segments. Moreover, a secondary duct in addition to 

 the primary Wolffian duct either remains on either side of the 

 Wolffian bodies, at that point where it communicates with 

 the Wolffian duct, or arises through the union of the transverse 

 excretory ducts. 



In the Amniota the Wolffian bodies 

 are permanent, but in the Amnia they do 

 not persist beyond the embryonic period 

 (see Fig. 75). The permanent kidneys 

 arise from the Wolffian ducts in the form 

 of a bud, near the opening into the cloaca. 



In the reptiles the kidneys are placed 

 far back and generally in the neighbour- 

 hood of the cloaca, and possess a consider- 

 able number of longitudinal convolutions, 

 or lobes. The lizards and tortoises, like 

 the amphibians, have a bladder springing 

 from the wall of the cloaca. 



In birds the kidneys are embedded in 

 the cavity between the transverse processes 

 of the coccygeal vertebrae and consist 

 usually of three lobes, sometimes united ; 

 the ureters, which generally originate at 

 the inner margin, open separately into the 

 cloaca. The development of the mam- 

 malian kidneys does not differ from that 

 of the reptiles and birds. 1 At first the kidney is unilobular ; 

 later it is divided into lobes through separation of the glandular 

 parenchyma, whereby the tubuli uriniferi in each lobe (see Fig. 

 76) combine to form a papilla, and the renal calyces unite to 

 form the pelvis of the kidney (see Fig. 76). The number of 

 lobes varies considerably but can always be ascertained from 

 the number of the different papillae, simple and compound. 



The seals, bear and otter possess a small number of dis- 



1 C. Gegenbauer, Vergl. Anat., p. 867. 



FIG. 75. Wolffian bodies 

 of the human em- 

 bryo. (Kobelt.) u, 

 Tubuli urinif. ; m, 

 Miillerian duct ; w, 

 Wolffian duct. 



