142 Prof. M'Intosh on the 



the lower margin to the yolk-sac. The pectorals are nearly- 

 alike, and the ventrals are generally absent. Thus the 

 young cod, haddock, whiting, ling, rockling, gurnard, flounder, 

 dab, turbot, plaice, and others have a tolerably close resem- 

 blance. They are all nourished in this tadpole- stage by the 

 small yolk-sac, and thereafter find the same minute food in 

 the sea around them. Yet the five former chiefly seek in 

 adult life the bottom waters ; the sixth is a mid- water or 

 bottom fish ; while the four last-named are characteristically 

 so_, often lying buried in the sand. 



During growth various modifications take place in the 

 young fishes, some of them being probably adapted for their 

 temporary sojourn in the upper regions of the water, while 

 others may be due to heredity. As development of the 

 muscular and other systems proceeds, and as each little fish 

 acquires greater powers of locomotion, the fins most used in 

 balancing increase in size. Thus the pectorals of the young 

 salmon, cod, haddock, whiting, and especially the gurnard 

 are disproportionately large in the succeeding stage, probably 

 because such enables them to capture their pelagic prey more 

 readily and with greater certainty. Their heads and eyes 

 are also comparatively large. 



In connexion with the development of the fins it is inter- 

 esting that some pelagic fishes, whose habits at present are 

 vaguely known, are remarkable for certain peculiarities in 

 their fins. Thus, in the oar-fish {Regalecus Banhsii) the 

 pectorals are of moderate size, while the slender ventrals are 

 enormously elongated and tipped with a flattened blade, so 

 that in outline they somewhat resemble a painter's maul-stick. 

 It is not known whether the fish uses these as tactile organs, 

 as the hump-backed whale is said to use its great flippers, to 

 avoid being beached, or otherwise ; but they would appear to 

 form an efficient means for sounding the distance from the 

 bottom or other solid structure. 



Now a remarkable change takes place in the fins of two 

 well-known fishes, one of which is of considerable commercial 

 importance, viz. the ling; and further examination will 

 probably reveal a similar condition in other forms, such as the 

 cod. Indeed Alex. Agassiz * figures a young fish with 

 attenuate and elongate ventrals, and which he conjectures to 

 be a young cod. 



After the early tadpole-stage of the ling already mentioned, 

 and in which it corresponds in outline with the young of 

 other food-fishes, though it is differentiated by peculiar dull 

 yellow pigment, it seeks its way downward as it grows larger. 



* Proc. Amer. Acad. Nat. Sc. xvii. p. 296, pi. viii. tigs. 4 and 6. 



