314 LAMARCK, HIS LIFE AND WORK 
to approach nearer the edge of the water. In this 
situation, receiving more light 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 front 
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 
