CHAPTEK XVI. 



DEVELOPMENT OF THE WOLFFIAN 

 NEYS, AND INTERNAL ORGANS 

 TION. 



BODIES, KID- 

 OF GENERA- 



THE first trace of a urinary apparatus in tho embryo consists of two 

 long, fusiform organs, which make their appearance in the abdomen at 

 a very early period, one on each side the spinal column, and which are 

 known by the name of the Wolffian bodies. They are fully formed, in 

 the human subject, toward the end of the first month (Coste), at which 

 time they are the largest organs in the abdomen, extending from just 

 below the heart, nearly to the posterior extremity of the body. In the 

 foetal pig, when thirteen or fourteen millimetres in length, the Wolffian 

 bodies are rounded and kidney-shaped, and oc- 

 cupy a large part of the abdominal cavity. Their 

 combined weight is at this time a little over 3 per 

 cent, of that of the entire body ; a proportion 

 which is seven or eight times as large as that of 

 the kidneys in the adult condition. There are, 

 indeed, at this period only three organs of no- 

 ticeable size in the abdomen, namely, the liver, 

 which has begun to be formed at the upper part 

 of the abdominal cavity ; the intestine, which is 

 already somewhat convoluted, and occupies a 

 central position ; and the Wolffian bodies, which 

 project on each side the spinal column. 



The Wolffian bodies, in their intimate structure, 

 closely resemble the adult kidney. They consist 

 of secreting tubules, lined with epithelium, run- 

 ning transversely from the inner to the outer edges 

 of the organs, and terminating at their extremities by rounded dilata- 

 tions. Into each of these dilated extremities is received a globular coil 

 of capillary bloodvessels, or glomerulus, similar to those of the kidney. 

 The tubules of the Wolffian body empty into a common excretory duct, 

 which leaves the organ at its lower extremity, and communicates with 

 the intestinal canal, at the point where the diverticulum of the allantois 

 is given off, and where the urinary bladder is afterward to be situated. 

 The principal distinction in structure, between the Wolffian bodies and 

 the kidneys, consists in the size of the tubules and of their glomernli ; 

 these elements being considerably larger in the Wolffian body than in 



PIG, 13 milli- 

 metres long; from a spe- 

 cimen in the author's pos- 

 session. 1. Heart. 2. An- 

 terior limb. 3. Posterior 

 limb. 4. Wolffian body. 

 The abdominal walls have 

 been cut away, in order 

 to show the position of 

 the Wolfflan bodies. 



the kidney. In the 

 ( 784 ) 



foetal pig, when 3j or 4 centimetres in length, 



