120 ZOOLOGICAL PHILOSOPHY 



its race of continually stretching and lengthening its legs, results in 

 the individuals of this race becoming raised as though on stilts, and 

 gradually obtaining long, bare legs, denuded of feathers up to the 

 thighs and often higher still. {Système des Animaux sans vertèbres, p. 14. ) 



We note again that this same bird wants to fish without wetting 

 its body, and is thus obhged to make continual efforts to lengthen 

 its neck. Now these habitual efforts in this individual and its race 

 must have resulted in course of time in a remarkable lengthening, 

 as indeed we actually find in the long necks of all water-side birds. 



If some swimming birds like the swan and goose have short legs 

 and yet a very long neck, the reason is that these birds while moving 

 about on the water acquire the habit of plunging their head as deeply 

 as they can into it in order to get the aquatic larvae and various 

 animals on which they feed ; whereas they make no effort to lengthen 

 their legs. 



If an animal, for the satisfaction of its needs, makes repeated efforts 

 to lengthen its tongue, it will acquire a considerable length (ant-eater, 

 green-woodpecker) ; if it requires to seize anything with this same 

 organ, its tongue will then divide and become forked. Proofs of my 

 statement are found in the humming-birds which use their tongues 

 for grasping things, and in lizards and snakes which use theirs to 

 palpate and identify objects in front of them. 



Needs which are always brought about by the environment, and the 

 subsequent continued efforts to satisfy them, are not hmited in their 

 results to a mere modification, that is to say, an increase or decrease 

 of the size and capacity of organs ; but they may even go so far as 

 to extinguish organs, when any of these needs make such a course 

 necessary. 



Fishes, which habitually swim in large masses of water, have need of 

 lateral vision ; and, as a matter of fact, their eyes are placed on the 

 sides of their head. Their body, which is more or less flattened 

 according to the species, has its edges perpendicular to the plane 

 of the water ; and their eyes are placed so that there is one on each 

 flattened side. But such fishes as are forced by their habits to be 

 constantly approaching the shore, and especially sUghtlv inclined or 

 gently sloping beaches, have been compelled to swim on their flattened 

 surfaces in order to make a close approach to the water's edge. In 

 this position, they receive more light from above than below and stand 

 in special need of paying constant attention to what is passing above 

 them ; this requirement has forced one of their eyes to undergo a 

 sort of displacement, and to assume the very remarkable position 

 found in the soles, turbots, dabs, etc. {Pleuronectes and Achirus). The 

 position of these eyes is not symmetrical, because it results from an 



