LAMARCK'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. 



" If 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 larvae 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 species, 

 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 



