DEVELOPMENT OF THE URINARY ORGANS. 



1937 



of the foetus, to the formation of certain structures and parts of the excretory canals of the 

 sexual glands. In the male the Wolffian duct and tubules persist chiefly as the vas deferens and 

 the epididymis ; in the female, in whom the 

 atrophy is more complete, these remains are 

 represented principally by the epoophoron and 

 Gartner's duct. In both sexes certain ad- 

 ditional rudimentary organs — the paradidy- 

 mis in the male and the paroophoron in the 

 female — are derived from the tubules of the 

 sexual segment of the Wolffian body. A more 

 detailed account of these transformations is 

 given in connection with the development of 

 the reproductive organs (page 2037 and Fig. 

 1719). 



Fig. 1642 



Stroma 



Primary collecting 

 tubules opening 

 into subdivisions 

 of pelvis 



Renal pelvis 



Malpighian body 



Malpighian 

 corpuscle of 



?*- atrophic 

 Wolffian 

 body 



Longitudinal section through developing kidney; por- 

 tion of atrophic Wolffian body is seen below. X 35. 



The Metanephros or Kidney, — 

 The development of the definitive kidney 

 in mammals begins as a pouch-like out- 

 growth from the posterior wall of the 

 Wolffian duct, a short distance above its 

 termination into the cloaca. In man the 

 renal diverticulum makes its appearance 

 during the fourth week, at which time 

 the embryo measures from 6-7 mm. in 

 length. At first short and wide, the stalk 

 of the pyriform sac soon becomes tubu- 

 lar, growing upward and backward into 

 the mesoblast of the posterior body-wall. 

 This stalk rapidly elongates, and termi- 

 nates above in a blind club-shaped ex- 

 tremity which after a time lies behind the 

 upper atrophic segment of the Wolfifian 

 body. The tubular duct becomes the 



ureter and its dilated end-segment the renal pelvis. The latter is surrounded by a 

 sharply defined oval area of compact mesoblast that is intimately concerned in the 



production of the convo- 

 FiG. 1643. luted kidney-tubules (of 



Ampullary terminations of ^,,-^ which aS yet UO trace is 



primary collecting tubules \^^_^^S^;-:^>1^^?^^^^^^,^ present), and heuce is 



termed xki^renal blastema. 

 From the ventral and 

 dorsal walls of the primi- 

 tive pelvis, which is com- 

 pressed from before back- 

 ward, a number of hollow 

 sprouts grow into the 

 surrounding mesoblastic 

 stroma. Each is a short 

 cylinder that terminates 

 in a slight dilatation. At 

 first few, these sprouts in- 

 crease rapidly in number 

 as well as in length, and 

 by repeated dichotomous 

 division give rise to a sys- 



Developing j^v 

 Malpighian i^ 

 bodies 



Primary 

 collecting 

 tube 



Loops 

 Henle 



Large col- 

 lecting duct 





tem of branching canals 



Section of developing kidney, showing formation of urinifer- 

 ous tubules and collecting canals. X loo. 



that later are represented 

 by the straight collecting- 

 tubules of the kidney. 

 Concerning the ori- 

 gin of the remaining portions of the uriniferous tubules two opposed views obtain. 



According to the one, all parts of these canals develop as direct continuations of the 



122 



