DEVELOPMENT OF KIDNEYS AND FAT-BODIES IN THE FROG. 141 



in size, but show no marked dilatations such as are present at 

 the earlier stage. 



During the metamorphosis the degeneration of the head kidney 

 proceeds rapidly ; the whole organ shrinks greatly in size, the cells 

 lose their outlines, and pigment appears in and between them. As 

 was first shown by Hoffmann,* the first, and a little later the second, 

 nephrostome closes up and disappears ; the third, or most posterior 

 nephrostome, persists for a time, but ultimately shares the same fate 

 and disappears. 



The condition of the head kidney in a frog shortly before the 

 disappearance of the tail is shown in Fig. 5, N A. At this stage the 

 head kidney consists of a small group of narrow convoluted tubules 

 with pigmented walls ; the two anterior nephrostomes have dis- 

 appeared, but the third or hindmost one is still present, and opens 

 into the body cavity. 



In a frog at the end of the first year the head kidney is almost 

 obliterated, and consists merely of a few indistinct cells surrounded 

 by pigment : all three nephrostomes have disappeared. 



Concerning the changes undergone by the archinephric duct, or 

 duct of the head kidney, our own observations are very imperfect, 

 but are perhaps worth recording, inasmuch as they confirm, so far 

 as they go, the only account with which we are acquainted of the 

 development of the Wolffian and Miillerian ducts in the frog, i.e., 

 the exceedingly careful and valuable description given by Hoffmann 

 in the paper already quoted.! 



The archinephric duct is, as we have seen, from the first in direct 

 connection with the head kidney. On the formation of the tubules 

 of the "Wolffian body, which first appear in tadpoles of about 12 mm. 

 length, these tubules open into the duct, so that the archinephric 

 duct for a time acts as the duct for both the head kidney and 

 the Wolffian body. At the time when the head kidney begins to 

 degenerate (Fig. 6), the part of the archinephric duct between the 

 head kidney and the anterior end of the Wolffian body (cf. Figs. 

 1 and 8, N D) becomes much flattened dorso-ventrally, and its 

 lumen almost completely obliterated ; and it is very possible that, as 

 suggested above, this obstruction or obliteration of the lumen of 



* Hoffmann, loc. cit., p. 594. 



I Hoffmann, loc. cit., pp. 594-099. 



