EAMARCK’S THEORY OF DESCENT 313 
and in those of its race have enabled them, after a 
time, to singularly elongate them—as, indeed, is 
proved by the long neck of all shore birds. 
“Tf any swimming birds, such as the swan and the 
goose, whose legs are short, nevertheless have a 
very long neck, it is because these birds in swim- 
ming on the surface of the water have the habit 
of plunging their head down as far as they can, to 
catch aquatic larve and different animalcules for food, 
and because they make no effort to lengthen their 
legs. 
‘When an animal to satisfy its wants makes re- 
peated efforts to elongate its tongue, it will acquire 
a considerable length (the ant-eater, green wood- 
pecker); when it is obliged to seize anything with 
this same organ, then its tongue will divide and be- 
come forked. That of the humming-birds, which 
seize with their tongue, and that of the lizard and 
serpents, which use it to feel and examine objects in 
front of them, are proofs of what I advocate. 
“ Wants, always occasioned by circumstances, and 
followed by sustained efforts to satisfy them, are not 
limited in results, in modifying—that is to say, in in- 
creasing or diminishing—the extent and the faculties 
of organs; but they also come to displace these same 
organs when certain of these wants become a neces- 
sity. 
“The fishes which habitually swim in large bodies 
of water, having need of seeing laterally, have, in fact, 
their eyes placed on the sides of the head. Their 
bodies, more or less flattened according to the sfeczes, 
have their sides perpendicular to the plane of the 
water, and their eyes are placed in such a way that 
there is an eye on each flattened side. But those 
fishes whose habits place them under the necessity of 
constantly approaching the shores, and especially the 
shelving banks or where the slope is slight, have been 
forced to swim on their flattened faces, so as to be able 
