1894.] TELEOSTEAN MOEPHOLOGY. 421 



The next featui-e is the relative size of the eye, and it may at 

 once be said that in the enlargement of this organ M. abyssonim 

 exhibits a character equally associated in Gadoids with either an 

 abysmal or a Boreal habitat. Gaclus saida may be taken as an 

 instance of the last, as one of the few Gadoids which are known 

 to be confined to Northern regions and which have not 

 hitherto been met with in deep water. Speaking generally, it may 

 be said that all Gadoids have rather large eyes, and it is question- 

 able whether their reduction in the more littoral forms, such as 

 some of the Motellce, may not be as much illustrative of modification 

 in one direction as their enlargement in the deep-sea forms appears 

 to be in another. This group of fishes appears, in fact, to be the 

 present representatives of a stock that had become adapted for 

 life at moderate depths rather than in either deep water or at the 

 extreme margin. 



With regard to the characters of the alimentary viscera a 

 reduction of the length of the gut has been shown by Dr. Giinther^ 

 to characterize a deep-sea member of the Percoid fishes ; but I am 

 not awai'e of any observation that bears on the relative strength 

 of the walls of the intestine. It is evident, however, from their 

 fragility in the species before us that life would be impossible in a 

 region exposed to any violent action of the tide, nor is it easy to 

 understand that the fish could display any great activity, without 

 risk of internal injury. That it is not an active fish, as compared 

 with its congener, may be judged from the reduction of the caudal 

 peduncle and fin, and by the attenuation of the whole caudal 

 region, a character we find invariably present both in deep-sea and 

 Northern Gadoids. The same may be said of the elongation of 

 the body, which carries with it the increase in the number of the 

 vertebrae and of the rays of the dorsal and anal fins, and it will be 

 remembered that CoUett found a constant increase in the number 

 of these structures in the more Northern examples of a series of 

 Hippoglossoides platessoides ^. 



A point which appears worthy of a moment's notice is the 

 pigmentation of the mucous membrane of the mouth and of the 

 peritoneum. It is a matter of common knowledge that these 

 structures are more" or less black in deep-sea fishes, whereas in 

 their more littoral allies they are usually destitute of dark 

 pigment, and this is well illustrated by comparing the two species 

 of Molva. We know that whatever light there may be in the 

 abysses of the ocean -is at all events not directly derived from that 

 which illuminates the surface. Without committing ourselves to 

 an opinion of the value of any particular theory, we may be 

 inclined to accept the broad fact that there is a connection 

 between light and pigmentation, and, in the case of flat-fishes, we 

 are familar with attempts which have been made from time to 

 time, with more or less success, to demonstrate this connection. 

 Passing from external to internal pigmentation, if we open the 



1 ' Cliallenger ' Reports, vol. xxii. p. 14. 



2 'Norwegian North Atlantic Expedition, Fishes,' Ohristiania, 1880, p. 147. 



Proc. Zool. Soc— 1894, No. XXVIII. 28 



