460 URO-GENITAL SYSTEM. 



tions we shall presently study when we consider the placent u 

 We will in this place only mention that the allautois and its 

 canal, the urachus, both disappear in the adult. The inferior 

 portion of the canal alone remains, and being developed 

 to an enormous size, constitutes the reservoir, called the 

 bladder. 



This rapid review of the origin of the genital and urinary 

 organs exhibits a close relationship between these two sys- 

 tems, and consequently teaches the close analogy between 

 their epitheliums ; since these mucous surfaces always origi- 

 nate from the epithelium of the sinus uro-yenitalis, which 

 latter is an offshoot from the intestinal epithelium, that is, 

 the internal layer of the blastoderm. 



We shall study in succession the urinary system and the 

 genital system of the male and the female. We shall else- 

 where recur to the embryological conditions of the two latter, 

 which alone furnish facts that establish the homology of the 

 organs of the two sexes. 



I. URINARY APPARATUS. 



A. Secretion of urine. 



In their structure the canals or tubes which compose the 

 renal parenchyma resemble the sudoriferous glands. These 

 are straight tubules in the medullary portion of the kidney 

 (ducts of Bellini, Fig. 125), then becoming convoluted or 

 twisted together (ducts of Ferrein) in the cortical substance. 1 



1 The connections of the straight tubules, of the convoluted 

 tubules (tubuli contorti), and of the glomeruli (Malpighian cor- 

 puscles) of the kidney, especially demonstrated by Schumlansky, 

 Bowman, and Isaacs, have met with formidable antagonism from 

 Miiller and Henle. Henle especially has undertaken to describe 

 some looped tubules among the uririiferous tubes, which he con- 

 sidered as terminating in culs-de-sac, or dividing into smaller 

 tubuli. There are, indeed, very remarkable looped tubules in the 

 kidney, but a study of these tubules, called tubules of Henle, 

 undertaken by Kblliker, Zawarickin, and especially Schweigger- 

 Seidel, has demonstrated that these formed no separate system, as 

 was formerly supposed by Henle (see " Traite" d' Anatomic," by 

 Cruveillier and M. See. 4th edition, 1869). By the action of 

 acids on the substance of the kidney, Schweigger-Seidel was the 

 first to show that Heule's tubules have the most intimate connection 

 with the classical straight and convoluted tubules of the kidney, and 

 that they are not in the least degree blood-vessels, as Chrzon- 



