l8 THE SENSES OF ANIMALS 



of the lower jaw, and it can thus be said that even if these 

 reptiles do not have ears, they can "hear" in a rather 

 specialized way. At the same time it is very doubtful if 

 snakes truly hear the sounds made by a snake charmer's 

 pipe; it is more likely that the rhythmic movements made 

 by a snake under these conditions are due to the eyes 

 being able to follow the side to side motions made by the 

 charmer himself. My own experiments will be referred to 

 later. 



Although snakes use their tongues to pick up particles of 

 scent, there is no evidence that taste is present. Many snakes 

 eat toads which are known to have an unpleasant taste. It 

 is therefore probable that snakes and most likely lizards as 

 well, depend much upon their sense of smell, though lizards 

 rely on scent to a lesser degree, their eyesight being very 

 acute indeed. 



The vast world of fishes presents some interesting sense 

 features. Generally speaking, most of the fishes can see well, 

 but there are some puzzles in the cases of some deep sea 

 species which live in almost total darkness yet they have 

 quite large eyes. There are, too, certain fishes that dwell in 

 caves and which are known to be blind. The sense of smell 

 is very well developed in fish as widely different as sharks 

 and trout ; and it seems more than likely that while sight is 

 used (and used efficiently) when water is clear; in muddy 

 water, through which light penetrates indifferently, fish fall 

 back on their olfactory sense to locate food. The sense of 

 taste is well developed. 



It is a commonplace occurrence to hear anglers say that 

 voices should be kept low when fishing, in case the fish will 

 thereby be disturbed ; but throughout a lifetime of anghng 

 I have never had reason to think that ordinary conversation 

 has any effect at all on the behaviour of fish. Nevertheless, 

 fishes are extremely susceptible to vibrations — particularly in 

 the water, or on the land immediately adjoining the water ; 

 and they possess highly specialized nervous equipment which 

 responds to vibrations and thus brings about escape be- 

 haviour of one kind or another. The mechanism involved in 

 this kind of sensory perception is known as the "lateral line" 

 and it will be fully described in Part II. 



