140 
ARTHUR E. GILES. 
thinking that he had traced in the pike the larval organ into 
the adult part of the kidney called by Hyrtl the pronephros ; 
and his final conclusion was “ that the pronephros, though 
found in the larvae or embryos of almost all the Ichthyopsida, 
except the Elasmobranchii, is always a purely larval organ, 
which never constitutes an active part of the excretory system 
in the adult state.” But Balfour did not apparently regard it 
as possible that the pronephros might continue in the Ich- 
thyopsida in a modified condition, but thought that if it did 
not persist Avith at least its original structure, if not its original 
function, it must have disappeared altogether. He was, how- 
ever, led to this conclusion by the study, not of their develop- 
ment, but of their adult structure. 
But it seems to me, from a consideration of the state of 
things in the tadpole and young Frog as above described, that 
it is not at all necessary that the pronephros, if it persist, 
should retain its original structure any more than its original 
function ; that it is quite possible that Rosenberg’s observa- 
tions were correct, since the only argument adduced against 
them is this alteration of structure, and that there is nothing 
in Balfour’s observations on the Ganoids and Teleosteans to 
contradict them. The fate of the pronephros in Teleosteans 
and Ganoids is, from this standpoint, closely analogous to that 
in the tadpole, except that in the latter it undergoes yet 
further modification in becoming quite separated from the true 
kidney and attached permanently to the genital organ. 
The fact that the pronephros does persist in a modified form 
seems to me in nowise to detract from but rather to add to 
the probability of Gegenbauer’s views being correct, namely, 
that the pronephros is the primitive excretory organ of the 
Chordata, and that its substitute in existing Vertebrata, the 
mesonephros, is phylogenetically a more recent organ. 
I may sum up my conclusions as follows : 
I. The fat-bodies in the Frog, and hence presumably in 
allied Amphibians, are formed by a fatty degeneration, not 
of the anterior end of the genital organs, but of original 
kidney structure. 
