82 Vertebrate Embryology 



irregularly twisted tubules, which have separated from 

 the duct, and which soon disappear completely. 



" Opposite the head kidney an irregular sacculated 

 outgrowth, the glomerulus, arises from the aorta on each 

 side (Figs. 28 and 31, GM); this appears first at about 

 the time of hatching, and its development keeps pace 

 with that of the head kidney. It lies immediately oppo- 

 site the nephrostomes, and very close to these, though 

 not touching them. It begins to diminish in size at 

 about the same time as the head kidney. At the time 



Fig. 30. — Diagrams to illustrate the development of the 

 HEAD-KIDNEY. (Somewhat altered from Morgan.) 



of the metamorphosis (Fig. 29, GM) it is very small, 

 and after the first year it can no longer be recognized. 

 Its close relation to the head kidney, and the fact that 

 its growth and subsequent degeneration keep pace with 

 those of the head kidney, point to a close physiological 

 connection between the two organs, though it is not 

 easy to imagine what precise function the glomerulus 

 subserves. 



3. The Wolffian Body 



" The Wolffian body, or kidney, first appears in tad- 

 poles of from 10 to 12 mm. in length. It arises on each 

 side as a series of small solid masses of mesoblast cells 



