240 THE SENSE-ORGANS AND PERCEPTION OF FISHES. 



Filamentous fins similar to tliose of tlie rocklings are found in 

 Protopterus annectens, in whicli botli the pectoral and pelvic fins 

 have this structure. Through the courtesy of Mr. Wells I was 

 enabled to watch the mode of feeding of this fish in the Brighton 

 Aquarium. The fins are used in a manner somewhat different from 

 that of the rockling, which merely extends the fins at right angles 

 to the body, and swims wildly about until they happen to touch the 

 food. Proto-pterus , on the other hand, whips with them on the bottom 

 of the tank until the food is struck. The tail also of this fish is, 

 perhaps, used for seeking food, but this was not clearly established. 



In connection with the sense of touch, the mode of feeding of the 

 soles may be fitly described. The sole feeds in a manner peculiar 

 to itself, and unlike that of any other fishes which have come under 

 my notice. As already stated, it remains buried by day, and generally 

 speaking, if the sand be fine its body is completely covered. When 

 shrimps or pieces of other food are thrown in, after an interval the 

 soles perceive it -, they then give a writhing jump or succession of 

 jumps from the bottom of the tank, and begin to search on the 

 ground. When searching for food the upper (right) side of the sole 

 is nearly always covered with a coating of sand so uniform that little 

 or none of the skin can be seen. There can, I think, be little doubt 

 that this sand sticks to the body owing to an outpouring of mucus 

 on the surface of the skin, which probably occurs when the smell of 

 food is perceived, and is comparable with the watering of the mouth 

 in ourselves.* This covering of sand is no doubt dusted over them 

 by these energetic movements, but it only adheres when the sole is 

 searching for food. At night, for example, when the soles are 

 active, they carry no sand. The coating of sand must be pretty 

 firmly attached, for if a sanded sole is made to swim rapidly the 

 covering of sand remains. 



In seaching for food the sole creeps about on the bottom by means 

 of the fringe of fin-rays with which its body is edged, and thus 

 slowly moving, it raises its head upwards and sideways, and gently 

 pats the ground at intervals, feeling the objects in its path with the 

 peculiar villiform papillae which cover the lower (left) side of its 

 head and face. In this way it will examine the whole surface of 

 the floor of the tank, stopping and going back to investigate pieces 

 of stick, string, or other objects which it feels below its cheek. As 

 already stated, the sole appears to be unable to find food that does 

 not lie on the bottom, and will not succeed in finding food suspended 



* At the moment when a conger lying still first perceives tlie smell of foodj he generally 

 shakes himself, and takes a gulping inspiration, freeing a variable quantity of mucus from 

 the skin and pharynx, which floats up through the water, owing to small bubbles of gas 

 which are enclosed in it. 



