130 ARTHUR E. GILES. 



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 : — 



1. 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. 



2. The part of the kidney which undergoes this conversion into 

 fat-body is the pronephros or head kidney. 



3. It seems very probable from analogy, and from the researches 

 of Rosenberg, that the structure in front of the true kidney in 

 Ganoids and Teleostei, described by Balfour as lymphatic tissue, is 

 the persistent but structurally and functionally modified pronephros. 



4. The fact that a part of the kidney undergoes such a remarkable 

 change, the rest remaining normal and functional, is an additional 

 argument in support of the view that the pronephros has a different 

 phylogenetic history from the mesonephros, and that it is more 

 ancestral. 



It only remains for me to perform the pleasant duty of expressing 

 my warm thanks to Professor A. Milnes Marshal] for the uniform 

 and stimulating kindness with which he has helped me in this 

 short research by suggestions and criticisms; he has been good 

 enough to go over my specimens with me, and to discuss with 

 me my results. 



I desire also to express my obligations to my friend Dr. G. 

 Herbert Fowler for much valuable and practical assistance. 



My thanks are further due to Professor Stirling, under whose 

 direction the work has been done. 



