420 MR. B. W. L. HOLT STUDIES IN [May 1, 



other baud, in the Birkelange the so-called head-kidney is more 

 definite in outline, and its histological structure leaves no doubt 

 that it is perfectly functional. In the Ling the proportion of 

 reniforrn matter is much less, but the head-kidney does not appear 

 to be wholly functionless. 



The Reproductive Organs. — Three specimens examined proved to 

 be females. The ovaries are much like those of the Ling. I rom 

 their condition it appears probable that the species spawns off 

 Iceland and Faroe late in the summer or in the autumn. 



The Skeleton. — One of the Faroe specimens has 78 vertebra, the 

 rirst complete haemal arch occurring on the 32nd. Lilljeborg 

 gives the total number as 78-79, of which 30-31 belong to the 

 trunk. In other respects the skeleton is much like that of the 

 Ling. 



Morphological Considerations. 



It appears that we have before us a form very closely allied to 

 the common species, and in which almost all the distinctive 

 characters are illustrative of specialization along one definite line. 

 To take them seriatim, we may consider first the relative length of 

 the jaws. 



The protrusion of the lower jaw is a feature most obviously 

 associated with the feeding-habits of the fish, and the fact that 

 the Northern Gadoids usually exhibit this character might be 

 found, could the matter be satisfactorily investigated, to indicate 

 nothing more than that the food-supply available in the higher 

 latitudes is not adapted to the requirements of bottom-feeders. 

 At the same time the protrusion of the lower jaw in the larvae of 

 all Teleosteans that have been studied may indicate that this 

 condition in the adult has an ancestral significance, such fish as 

 exhibit it being in this respect less specialized than others which 

 do not, though here again the pelagic habit of the said lame may 

 go far to prove the character to be merely one of adaptation. 

 Thus, like most other scientific facts in the present state of our 

 ignorance, we may derive therefrom whatever interpretation 

 appears most convenient to preconceived theory. That there is 

 no necessary connection in Gadoids between this character and an 

 abysmal habitat is sufficiently demonstrated by the Macrurida?, 

 but the fact remains that such association usually exists in the 

 less specialized members of the group (cf. Merlaccias, Mora, &c). 

 The reduction of the barbel is a character so obviously related to 

 the elongation of the lower jaw that it requires no separate 

 discussion, since it is difficult to see what benefit an "underhung" 

 fish could derive from such an appendage, however well developed. 

 Nevertheless the presence of a well-developed and functional 

 barbel in the closely-allied species with the shorter mandible 

 almost forces us to regard the appendage in M. abyssorum as 

 vestigial, and, if that be admitted, it is not difficult to arrive at a 

 conclusion as to which condition of the jaws is least indicative of 

 specialization. 



