1002 OF GENERATION. 



straight canals (2, 2) into the cloaca. Between their component shut sacs, 

 numbers of small points appear, which consist of little clusters of convoluted 

 vessels, exactly analogous to the Corpora Malpighiana of the true kidney. These 

 bodies remain as the permanent urinary organs of Fishes ; but in the higher 

 Vertebrata they give place to the true Kidneys, the development of which com- 

 mences in the Chick about the 5th day. These are seen on the 6th day, as 

 lobulated grayish masses (3), which seem to sprout from the outer edges of the 

 Wolffian bodies, but which are really independent formations springing from a 

 mass of blastema behind them ; and as they gradually increase in size and advance 

 in development, the Wolffian bodies retrograde ; so that, at the end of foatal life, the 

 only vestige of them is to be found as a shrunk rudiment, situated (in the male) near 

 the testes. The history of the development of the Urinary organs in the Human 

 embryo seems to correspond closely with the foregoing. The Wolffian bodies 

 begin to appear towards the end of the first month ; and it is in the course of the 

 7th week that the true Kidneys first present themselves. From the beginning of 

 the 3d month, the diminution in the size of the Wolffian bodies goes on paripassu 

 with the increase of the Kidneys ; and, at the time of birth, scarcely any traces 

 of the former can be found. At the end of the 3d month, the kidneys consist 

 of seven or eight lobes, the future pyramids; their excretory ducts still termi- 

 nate in the same canal, which receives those of the Wolffian bodies, and of the 

 sexual organs ; and this opens, with the rectum, into a sort of cloaca, or sinus 

 uro-genitalis, analogous to that which is permanent in the oviparous Vertebrata. 

 The Kidneys are at this time covered by the Suprarenal capsules, which 

 equal them in size ; about the 6th month, however, these have decreased, whilst 

 the kidneys have increased, so that their proportional weight is as 1 to 2. At 

 birth, the weight of the Kidneys is about three times that of the Supra- Renal 

 capsules, and they bear to the whole body the proportion of 1 to 80 ; in the 

 adult, however, they are no more than 1 to 240. The Corpora Wolffiana are, 

 when at their greatest development, the most vascular parts of the body next 

 to the liver ; four or five branches from the aorta are distributed to each, and 

 two veins are returned from each to the vena cava. The upper veins and their 

 corresponding arteries are converted into the Renal or emulgent vessels ; and 

 the lower into Spermatic vessels. The lobulated appearance of the kidney 

 gradually disappears ; partly in consequence of the condensation of the areolar 

 tissue which connects the different parts, and partly through the development of 

 additional tubuli in the interstices. The Urinary Bladder is formed quite inde- 

 pendently of the secreting apparatus, being a part of the allantois, which itself 

 serves as the receptacle for the urinary secretion formed by the Corpora 

 Wolffiana. The part of the tube below this forms the Cloaca, or common 

 termination of the intestinal and vesical apparatus. The sides of this cloaca, 

 however, gradually approach one another, so as to form a transverse partition, 

 which separates the Rectum from the Genito-urinary canal ; and the urethra of 

 the female is afterwards separated from the Vagina by a similar process. 



1008. The essential parts of the Generative Apparatus, namely, the Testes 

 in the male, and the Ovaria in the female, are first developed in immediate 

 proximity with the Corpora Wolffiana (Fig. 272, 5, 5), and have been supposed 

 to sprout forth from them ; this, however, is not really the case, as they have 

 an independent origin in a mass of blastema peculiar to themselves. They make 

 their first appearance in the Chick about the fourth day, as delicate striae on the 

 Wolffian bodies ; and at this period no difference can be detected between the 

 Testes and the Ovaria, which originate in precisely the same manner. Like 

 the kidneys, the germ-preparing organs increase in proportion with the dimi- 

 nution in the temporary structures ; at first, their efferent ducts open into those 

 of the Wolffian bodies, but they are subsequently separated by the formation of 

 a partition, like that which separates the rectum from the cloaca. In the 



