314 LAMARCK, HIS LIFE AND WORK 



to approach nearer the edge of the water. In this 

 situation, receiving more Hght from above than from 

 beneath, and having a special need of being always 

 attentive to what is going on above them, this need 

 has forced one of their eyes to undergo a kind of dis- 

 placement, and to assume the very singular situation 

 which is familiar to us in the soles, turbots, dabs, etc. 

 {Pleuronectes and Achirus). The situation of these 

 eyes is asymmetrical, because this results from an in- 

 complete change. Now, this change is entirely com- 

 pleted in the rays, where the transverse flattening of 

 the body is entirely horizontal, as also the head. 

 Also the eyes of the rays, both situated on the upper 

 side, have become symmetrical. 



" The serpents which glide along the surface of the 

 ground are obliged chiefly to see elevated objects, or 

 what are above their eyes. This necessity has brought 

 an influence to bear on the situation of the organs of 

 vision in these animals ; and, in fact, they have the 

 eyes placed in the lateral and upper parts of the head, 

 so as to easily perceive what is above or at their 

 sides ; but they only see for a short distance what is 

 in front of them. Moreover, forced to supply the 

 lack of ability to see and recognize what is in froat 

 of their head, and which might injure them, they 

 need only to feel such objects with the aid of their 

 tongue, which they are obliged to dart out with all 

 their power. This habit has not only contributed to 

 render the tongue slender, very long and retractile, 

 but has also led in a great number of species to its 

 division, so as to enable them to feel several objects 

 at once ; it has likewise allowed them to form an 

 opening at the end of their head, to enable the tongue 

 to dart out without their being obliged to open their 

 jaws. 



" Nothing is more remarkable than the result of 

 habits in the herbivorous mammals. 



" The quadruped to whom circumstances and the 



