46 HEAD KIDNEY OF TELEOSTEAN FISHES. 



permanently separated from all abdominal viscera before the com- 

 pletion of tlie raesonephros. Second^ from the manner in which the 

 head kidney is encased in bone, it appears that if what I am naming 

 head kidney is in reality a part of the body kidney grown forwards 

 (since it is functional), it must, to have taken up its position in the 

 head, have penetrated both the air-bladder and the scapular arch. 



Again, does the similar condition of the pronephros in a small 

 adult Cyclopterus and an old adult Dactylopterus, not indicate that 

 in some fishes (e. g. Dactylopterus) the degeneration of the organ in 

 question has not yet reached that point demonstrable in many ? 

 This seems to me to be a more natural view than to suppose that 

 any functional kidney occupying a position in the head is merely 

 the whole or part of the true body kidney translated from its normal 

 position. 



If, then, I establish the fact that the head kidney in Dactylop- 

 terus is in reality a functional pronephros persisting in the adult, the 

 statement of Balfour that such an organ does not exist must be 

 modified, and a compromise made between it and the older hypo- 

 thesis of Eosenberg, who first demonstrated that the head kidney 

 was the persistent pronephros. 



I think the above evidence, therefore, favours the conclusion that 

 in adult Teleosteans the renal function is performed in some 

 instances by the body kidney only ; in others by the head kidney 

 only ; and in others — probably a very limited number — by both the 

 body and head kidneys. Besides Dactylopterus, I am aware of only 

 one instance where the head kidney is described as possessing 

 tubules and Malpighian bodies, viz. in Fierasfer. (Carlo Emery, Le 

 Specie del Genere Fierasfer nel Golfo di Napoli, Leipzig, 1880). 



EXPLANATION OF PLATE I. 



Illustrating Mr. Calderwood's paper on '' The Head Kidney of 

 Teleostean Fishes." 



Fig. 1. — Transverse section of head kidney of an adult Dactylopterus. Zeiss' D, oc. 2. 



Fig. 2. — Transverse section of head kidney of adult Cyclopterus. Zeiss' D, oc. 2. 



Fig. 3. — Longitudinal section of pronephros of Cyclopterus embryo at thirteenth day. 

 Zeiss' D, oc. 2. 



Fig. 4. — Transverse section of head kidney of young adult Cyclopterus. Prom spirit 

 specimen. Zeiss' D, oc. 2. 



