FISHES 1345 



lowest fish, the little clear-bodied lancelet, pos- 

 sesses no brain whatever, and no organ of hearing is 

 developed, while the eyes are at the best of very sim- 

 ple and rudimentary structure. In other fishes, again, 

 the brain and nervous system not only acquire a 

 typical development, but the senses also advance in 

 perfection. The sense of sight is of perfect kind, 

 the eyes of fishes being adapted for seeing in the 

 dense medium in which they live; while the sense 

 of smell is also developed, although, curiously 

 enough, the nostrils, in all except two kinds of 

 fishes the hag-fishes and the curious Lepidosiren or 

 mud-fish are pocket-like in nature, and do not open 

 backward, as in higher animals, into the mouth. 

 The sense of taste is not exercised in a high degree 

 by fishes, and it is interesting to observe that the sense 

 of touch appears to reside especially in the sides of 

 the body, on which surfaces a well-marked line the 

 "lateral line" may be observed in most fishes. This 

 lateral line is connected with a series of canals or 

 sacs abundantly supplied with nerves. The function 

 of these organs is believed to be that of exercising 

 the sense of touch; and from the manner in which 

 many fishes swim against objects, and bring the sides 

 of their bodies in gentle contact with foreign objects, 

 there would seem to exist strong reasons for support- 

 ing the above idea. That fishes "hear" is a well- 

 known fact. No outer ear is developed, but an in- 

 ternal ear the essential part of the organ of hearing 

 is found in all fishes except the little lancelet. 



While the intelligence or instinct of fishes is not, 

 generally speaking, of a high order, there are not 



