462 Survey of Fishing- Grounds, West Coast of Ireland, 1890-1891. 



more interest. 3Io7-a mediterranea (loc. cit.) is referred to as possessed of this 

 organ also ; and one or two other fishes, not obtained during the Survey Expe- 

 dition, but known to inhabit considerable depths in the Mediterranean, have been 

 described as exhibiting a persistent pronephros in the same manner — notably 

 the various species of Fierasfer* and Dactylopterus volitans-\. Amongst pelagic 

 or shore fishes a head-kidney does, in some cases, exist, but, as pointed out by 

 Balfour in 1881, it has become degenerate, and is now functionless. Balfour J 

 examined the pike, eel, smelt, and angler in confirmation of his own previous 

 statement. The angler [Lophius piscatorius) is generally supposed to possess only 

 a head-kidney, and this organ is certainly functional. Parker, § however, in 

 supporting Balfour's conclusions, argued that this so-called head-kidney was in 

 reality the true body-kidney shifted forward so as to occupy the position of a 

 head-kidney. 



The condition described in the case of Dactylopterus has been considered as 

 pointing rather to the belief that a functional head-kidney as well as body-kidney 

 may exist ; because in the developing embryo the segmental duct and pronephros 

 are developed at a much earlier period than the mesonephros, and must be per- 

 manently separated from all abdominal viscera before the completion of the 

 mesonephros ; and, also because from the manner in whicli the head kidney is 

 incased in bone, any forward growth of a body-kidney towards this pronephric 

 position is rendered impossible. || 



The condition observed in Macrurus nipestris appears to us to strengthen the last 

 argument, and at the same time to indicate that, amongst deep-sea fishes, a 

 persistent and functional head-kidney seems to be much more common than it is 

 amongst fishes inhabiting shallow water. 



The conditions of life at great depths of the ocean is known to produce marked 

 modifications on the fauna. In many instances this modification takes the form 

 of degeneracy ; but, in others, as in the example under consideration, an ancestral 

 organ appears to be retained in its early condition. 



Section I. {vide, p. 450) 



(5.) Mouth inferior; infra-orbital ridge more or less distinct; dorsal spine 

 serrated. 



* Emery, C. " Le Specie del Genere Fierasfer nel Golfo di Napoli." Leipzig, 1880. 



t Calderwood, W. L. " Proe. Roy. Soc. Edinb.," xvii., 1890. 



X Balfour, F. M. " Quar. Jour. Mic. Sc," January, 1882. 



§ Parker, W. N. " Brit. Assoc. Reports," 1882, p. 577. 



II Calderwood, W. L. "Journal Mar. Biol. Assoc," vol. ii., No. 1 (N.S.), p. 43. 



