DEVELOPMENT OF KIDNEYS AND FAT BODIES IN THE FROG. 145 



40 mm. are shown in Fig. 1, N G, and in the tailed frog in Fig. 5, 

 N G. It is still present, though very small, at the end of the first 

 year, but is absent in frogs of the second year. 



Its position directly opposite the nephrostomes of the head kidney, 

 and the fact that its development, both progressive and retrogressive, 

 keeps pace with that of the head kidney, points to a close physiological 

 connection between the two organs ; though it is not easy to imagine 

 what precise function the glomerulus subserves. 



II. The Development of the Wolffian Body op, Kidney. 



1. The Formation of the Wolffian Tubules. — Like all previous 

 observers, we have found the early stages in the development of the 

 "Wolffian tubules in the frog extremely difficult to determine, and 

 our observations are by no means so complete as we could wish. 



Fiirbringer* describes the Wolffian tubules as arising in Urodeles 

 in the form of solid ingrowths of the peritoneal epithelium close to 

 the root of the mesentery. These form solid strings of cells, which 

 soon separate from the peritoneum, acquire a lumen, and become 

 convoluted tubes. 



Hoffmannf describes the development in Urodeles somewhat 

 differently. He agrees with Fiirbringer in describing the earliest stage 

 in the development of a Wolffian tubule as a solid ingrowth of peri- 

 toneal cells, but he differs from him in maintaining that the peritoneal 

 connection is retained and gives rise to the nephrostome through 

 which the Wolffian tubule opens into the ccelom. In this respect 

 he is in agreement with Goette and with Spengel. In Anura, Hoff- 

 mann describes the early stages as identical with those of Urodeles, 

 the nephrostomes arising as solid ingrowths of peritoneum, of which 

 the inner ends become tubular, acquire openings into the archi- 

 nephric duct, and then growing rapidly become much convoluted. 

 The Malpighian body is formed at the inner end of the nephrostomial 

 funnel, and after its formation the funnel separates off', and, according 

 to Hoffmann, ends blindly. 



Hoffmann and Sclenkaj lay stress on the fact that the Wolffian 

 tubules develope from behind forwards, appearing first at the extreme 



* Fiirbringer, loc. cit., pp. 54 et set/. 

 I Hoffmann, loc cit., pp. 573 and 592. 

 I Selenka, loc. cit., cf. especially Fig. 1. 



