3i8 LAMARCK, HIS LIFE AND WORK 



had not become the habitual action of the animals 

 which have exercised them. The observations made 

 on all the animals known will everywhere furnish 

 examples. 



" Can any of them be more striking than that which 

 the kangaroo offers us ? This animal, which carries its 

 young in its abdominal pouch, has adopted the habit 

 of holding itself erect, standing only on its hind feet 

 and tail, and only changing its position by a series of 

 leaps, in which it preserves its erect attitude so as not 

 to injure its young. 



" Let us see the result : 



" I. Its fore legs, of which it makes little use, and 

 on which it rests only during the instant when it 

 leaves its erect attitude, have never reached a de- 

 velopment proportionate to that of the other parts, 

 and have remained thin, very small, and weak ; 



" 2. The hind legs, almost continually in action, 

 both for supporting the body and for leaping, have, 

 on the contrary, obtained a considerable develop- 

 ment, and have become very large and strong ; 



" 3. Finally, the tail, which we see is of much use 

 in supporting the animal and in the performance of 

 its principal movements, has acquired at its base a 

 thickness and a strength extremely remarkable. 



" These well-known facts are assuredly well calcu- 

 lated to prove what results from the habitual use in 

 the animals of any organ or part ; and if, when there 

 is observed in an animal an organ especially well de- 

 veloped, strong, and powerful, it is supposed that its 

 habitual use has not produced it, that its continual 

 disuse will make it lose nothing, and, finally, that this 

 organ has always been such since the creation of the 

 species to which this animal belongs, I will ask why 

 our domestic ducks cannot fly like wild ducks — in a 

 word, I might cite a multitude of examples which 

 prove the differences in us resulting from the exercise 

 or lack of use of such of our organs, although these 



