128 ARTHUR E. GILES. 



body goes a step farther, since the primary connection with the 

 kidney is lost, while the vasa efferentia remain connected with both 

 kidney and testis. 



Again, the question may be asked, " Why should only a part 

 of the kidney structure undergo fatty degeneration — why should 

 not the meso- and meta-nephros share in the change 1 " The answer 

 would be even more difficult to find if, on the supposition that von 

 Wittich was right, such a question were asked concerning the genital 

 organs, for they are of equal value in all their parts, and when the 

 metamorphosis occurs no portion of them has had any reproductive 

 activity. But in the case of the pronephros it is different. It is 

 true that the nature and origin of the pronephros are still matters of 

 discussion, but it is at least evident that the pronephros is in many 

 respects different from the mesonephros ; that the former, in the 

 case of the frog and of all animals with a larval stage, has a period 

 of activity before the mesonephros appears at all, and in most cases 

 disappears as the latter begins to take on active functions. On the 

 other hand, in Vertebrates possessing no larval stage, the existence 

 of the pronephros is only dimly shadowed forth by rudimentary 

 traces, the meso- and meta-nephros performing all the excretory 

 functions from the first. 



The answer then to the question, " Why this change should occur 

 resulting in the formation of the fat-body," seems to be this — that 

 with the close of larval life the pronephros is no longer needed, and 

 in harmony with the pathological law that atrophy follows disuse, it 

 degenerates to the condition of fat-body. Doubtless, however, this 

 law is here so far modified that the fat-body still serves some useful 

 purpose in the organism, though what that purpose is is not at all 

 clear. It is in all probability an example of " change of function," 

 the later function being in some way nutritive. 



As to the distribution of fat-bodies — they are unknown outside 

 the Amphibian group. According to Stannius, Hoffmann, Wieders- 

 heim, and others, they are present in all Amphibians. We have 

 very little knowledge of their function beyond that they are con- 

 cerned in all probability with nutrition, serving as a reserve stock at 

 certain times of the year. They are differently placed in the several 

 groups in which they occur, and it is by no means certain whether 

 they are homologous structures in all cases. 



