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Show 1894.] TELEOSTEAN MORPHOLOGY. 421 The next feature is the relative size of the eye, and it m a y at once be said that in the enlargement of this organ M. abyssorum exhibits a character equally associated in Gadoids with either an abysmal or a Boreal habitat. Gadus 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 questionable 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. Giinther1 to characterize a deep-sea member of the Percoid fishes ; but I am not aware 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 w e 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 Collett found a constant increase in the number of these structures in the more Northern examples of a series of Hippoglossoides platessoides 2. 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. W e 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, w e may be inclined to accept the broad fact that there is a connection between light and pigmentation, and, in the case of flat-fishes, w e 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 ' Challenger' Reports, vol. xxii. p. 14. 2 'Norwegian North Atlantic Expedition, Fishes,' Christiania, 1880, p. 147. PROC. ZOOL. Soc-1894, No. XXVIII. 28 |