43 



The Head Kidney of Teleostean Fishes. 



By 

 W. li. C'alderwood. 



With Plate I. 



Until the year 1881, when Balfour wrote on the subject,* the 

 pronephros was generally believed to be a functional kidney, not 

 only in the larval condition, but also in those adult forms described 

 as possessing the organ. 



Balfour, in his more detailed paper, published later,t states that 

 in the fishes examined — -pike, eel, smelt, and angler — although the 

 pronephros had all the appearance, externally, of a true functional 

 kidney, no uriniferous tubules were present, and that a minute 

 examination only disclosed a degenerate trabecular tissue which he 

 describes as lymphatic. 



The angler (Lophius), it may be observed, is generally considered 

 to possess only a head kidney. This organ Balfour found to be in 

 a perfectly functional condition, but he declines to believe that it is 

 a persistent head kidney, and argues from the highly modified 

 structure of the fish that the organ in question is in reality the 

 mesonephros shifted forward from its normal position. He also 

 maintains that in adult Ganoids the head kidney has no longer a 

 renal function. His general conclusion, therefore, is, that since the 

 pronephros was only supposed to persist in Ganoids and Teleosteans, 

 it must be now considered as non-existent except in the embryonic 

 or larval conditions. 



Parker J also supports the conclusions of Balfour by stating that 

 in many instances the mesonephros has grown forward in front of 

 the air-bladder and taken the place of the pronephros. 



* The Pronephros of Teleosteans and Ganoids, Brit. Assoc. Reports, 1881, p. 721. 



t Quart. Journ. Micros. Science, January, 1882. 



% On the Kidneys of Teleosteans, Brit. Assoc. Report, 1882, p. 577. 



