238 THE SENSE-OEGANS AND PERCEPTION OP FISHES. 



feeding of the rockliug or pouting {Gadus luscus) can doubt tliat 

 tliese organs are employed for the discrimination of food-substances ; 

 but the fact already mentioned, that the rockling in which the 

 olfactory organs had been extirpated did not take any notice of food 

 that was not put close to it, points to the conclusion that they are 

 of service only in actual contact with the food itself. 



Sight. — In view of the fact that these fishes do not habitually re- 

 cognise food by sight it would be especially interesting to determine 

 what part in their economy is played by visual perceptions. Though 

 nocturnal animals, they all have functional eyes, which in the 

 congei', skates, and dog-fishes are as well developed as those of other 

 fishes (u. p. 228). In the angel-fish, torpedo, and soles the eyes 

 are, however, of small proportional size. Nevertheless, with the 

 exception of the dog-fish and skates, in which the pupil is covered in 

 daylight by the iris, there is nothing to suggest that there is any 

 difference between the eyesight of these forms and that of other 

 fishes. Positive evidence as to the class of objects which they dis- 

 tinguish is difiicult to obtain owing to the general absence of facial 

 or other expressions among fishes ; and it should always be remem- 

 bered that the fact that animals take no notice of objects is no 

 proof that they do not see them. For example, wrasses, mullet, 

 and other fishes with excellent sight take no notice of a handkerchief 

 suddenly flipped against the glass of the tank in which they are, 

 which would scare away a terrestrial animal ; but it is perfectly cer- 

 tain that they see the handkerchief, for they will snap at a worm 

 hanging by a thread or sticking to the outside of the glass. Simi- 

 larly they take no notice of a straight wire held up and waved out- 

 side the tank, but if the wire be bent into a sinuous curve like the 

 body of a swimming worm they (pollack) will often dash at the glass 

 in the attempt to seize it. It would appear, however, that fish are 

 by no means slow at gaining knowledge of this kind. A curious in- 

 stance of this occurred in the case of the rockling {Motella tricirrata) . 

 When I first began to observe the mode of feeding of this fish I 

 was inclined to believe that it did not see worms, &c., thrown in for 

 food. As mentioned above, it does not come towards them until they 

 have been for some time in the water, and then, moving its head and 

 fins, it swims wildly about until it comes in contact with the food, 

 even though it be hanging freely in the water directly in the line of 

 sight. But one of tliese fishes which has been living for some 

 months in a shallow tank has been constantly fed by persons leaning 

 over the top j and now when hungry not only comes up and splashes 

 about on the surface of the water as soon as any one approaches, but 

 will lift its head out of the water to snap at the fingers held above 

 the surface, which it obviously sees and recognises. When last ob- 



