276 NOTES AND MEMORANDA. 



no approach either to the Icelandic or New England hake, as regards 

 an exceptionally large number of fin-rays. 



The lean and emaciated condition of the specimen was, however, 

 very striking, especially in the head region, where not only the bony 

 ridges of the skull and cheeks projected sharply beneath the thin layer 

 of skin, but even the lines of sculpture of the superficial bones were 

 plainly recognisable. In a normal hake, with which I compared the 

 specimen, these details were quite invisible, and the bony ridges were 

 rounded off or hidden by the plumpness of the integument. In girth 

 and weight the albino was far inferior to the normally pigmented hake 

 of approximately equal length, as the following figures reveal : — 



Length, to base of caudal fin 



Length of head (snout to opercular spine) . 



Interorbital breadth 



Girth round head, just in front of pelvic fins 



Girth just behind the tenth anal fin-ray . 



Weiglit (gutted) . ... 



These data show that, although the length of the albino was only 

 4| per cent, less than that of the normal hake, the deficiency in girth 

 amounted to 11 per cent, and the deficiency in weight to 23 per cent. 



As the fish showed no signs of disease, I believe its lean condition 

 may be attributed with some confidence to the check placed upon 

 its catching powers by its conspicuous white colouration. Being a 

 predacious and nocturnal fish, the hake must depend largely for its 

 success in catching mackerel and other active prey upon its dusky 

 inconspicuous appearance. A white hake, on the other hand, would 

 be more easily avoided, especially at night, and would therefore catch 

 fewer fish. Hence the emaciated condition of this albino is particularly 

 interesting from the evidence it seems to afford of the operation of 

 natural selection as regards the colouration of fishes. 



In drawing this conclusion I have not overlooked the possibility 

 that the deficiency in skin pigment may have involved a thinning of 

 the skin, either as a physiological or congenital correlate, especially 

 as in the New England hake {M. bilinearis), which appears to be less 

 darkly pigmented than the European species, the ridges on the head 

 are described as being very conspicuous (Jordan and Evermann, Fishes 

 of North America, 1898, p. 2,530). The relative deficiency in the 

 weight of this albino fish appears to be far too great to admit of 

 this interpretation. Walter Garstang. 



