GENERAL FACTS ABOUT SEA FISH 17 



mailed head of the gurnard (Trigla), the flattened head of 

 the angler-fish (Lopkius), the attenuated head of the stickle- 

 back {Gasterosteus) and pipe-fish {Sygnathus), and the truncated 

 head of the wolf-fish [Anarrhicas). The conspicuous pro- 

 trusion of either jaw imparts a characteristic and distinctive 

 profile to the head of a fish. The greater length of the lower 

 jaw (as in the pollack and hake) is usually associated with 

 predatory habits ; the protrusion of the upper (as in the cod 

 and haddock) indicates that the fish feeds near the ground. 

 As these cases show, cases of either jaw protruding occur in 

 the same family. As a matter of embryological knowledge, 

 the lower jaw usually projects in the larval form of bony 

 fishes, but that would not, of course, indicate that we should 

 read these larval characters as a clue to ancestral peculiarities 

 since dropped and regard all bony fishes as originally predatory. 



Another feature that may conspicuously modify the outline 

 of the head is the presence of barbels, or beards, usually (as in 

 cod and red mullet) on the lower jaw, but sometimes (as in the 

 rocklings) on the upper as well, and in various number. The 

 finger-like front rays of the ventral fins in the gurnard bear 

 at first sight a close resemblance to these barbels, and no doubt 

 they perform much the same work when the fish is routing 

 in the shingle for its minute food ; but the two structures 

 are quite distinct and should not be confused. That the 

 barbels of fishes are highly sensitive nerve-centres can hardly 

 be doubted, but whether they are to be regarded as associated 

 with the sense of touch, or rather with that of taste, we do not 

 yet know. Dr. Bashford Dean inclines to the former view.* 



The eye of fishes, into the anatomy of which it is not the 



purpose of the present volume to enter in detail, is subject 



to considerable structural modification, and we find 



^ ' by experiment that the sense of sight predominates 



in some groups, while in others it is of secondary importance 



only, the fishes relying in this case chiefly on their scent. It 



* Fishes, Living and Fossil, p. 48. 



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