THE SENSE-ORGANS AND PERCEPTION OF FISHES. 239 



served, however, it still did not appear to have learnt to recognise a 

 worm swimming in the water, but only the presence of the person 

 feeding it. When it is remembered that this j&sh naturally hunts 

 by scent, the acquirement of this new instinct seems somewhat 

 remarkable, and suggests that it is not the vision which is defec- 

 tive, but the power of appreciation. Being a nocturnal animal, it 

 must be supposed to have never seen food, or to have seen it so 

 rarely that it made no impression on it. These considerations suggest 

 the possibility that these fishes may in the course of time learn to 

 distinguish food by sight as they are now habitually fed by day. 



There can be no doubt that soles also perceive objects approach- 

 ing them, for they will bury themselves if a stroke at them is made 

 with a lauding net ; yet they have no recognition of a worm hang- 

 ing by a thread immediately over their heads, and will not take it 

 even if it touch them, but continue to feel for it aimlessly on the 

 bottom of the tank, being aware of its presence by the sense of 

 smell. Soles, eels, and recklings, moreover, have a clear apprecia- 

 tion of light and darkness being always buried or hidden by day 

 (unless food is thrown in), but swimming freely about the tank like 

 other fish at night. When thus swimming at large they bury or 

 hide themselves if a light be flashed on them. Conger and loaches 

 have some appreciation of moving objects, and occasionally snap at 

 them, but their perceptions are extremely vague, as may be shown by 

 watching their attempts to take a piece of food trailed through the 

 water with a line. Their movements altogether are suggestive of a 

 blurred perception, and perhaps it may be that their eyes are capa- 

 ble of distinct vision under greater pressure or in less light or at a 

 greater distance. That greater pressure might produce an effect is 

 very possible, but on watching their movements at night with a 

 dark lantern, or in a tank from which the light was screened, there 

 was no perceptible difference in their aptitude in discovering food. 



None of these fishes have much apparent difl&culty in avoiding 

 obstacles, but as large obstacles seem to be easily avoided by the 

 same animals when deprived of sight, it may be doubted whether 

 this perception of obstacles is not as much obtained by general sen- 

 sation, especially of currents, as it is by sight. 



As to the sight of the sterlet no experiments have as yet been made. 



Touch. — In the recklings, as mentioned in this journal (N. S., i, 2, 

 p. 214), the pelvic fins are developed as special tactile organs, and 

 are used in the mode there described. By these organs they are not 

 only able to distinguish food-substances alone, for a rockling on brush- 

 ing with its pelvic fins against a piece of glass or a stone smeared 

 with vaseline, turus and examines it, clearly remarking the peculiar 

 feel of such surfaces. 



