LAMARCK'S THEORY OF DESCENT 



321 



vinced that the habits which the individuals of the 

 race of the ai were originally compelled to contract 

 have necessarily brought their organization into its 

 actual state. 



" Since continual exposure to dangers has at some 

 time compelled the individuals of this species to take 

 refuge in trees and to live in them permanently, and 

 then feed on their leaves, it is evident that then they 

 would give up making a multitude of movements 

 that animals which live on the ground perform. 



" All the needs of the ai would then be reduced to 

 seizing hold of the branches, to creeping along them or 

 to drawing them in so as to reach the leaves, and then 

 to remain on the tree in a kind of inaction, so as to 

 prevent falling. Besides, this kind of sluggishness 

 would be steadily provoked by the heat of the 

 climate ; for in warm-blooded animals the heat urges 

 them rather to repose than to activity. 



" Moreover, during a long period of time the indi- 

 viduals of the race of the ai having preserved the 

 habit of clinging to trees and of making only slow 

 and slightly varied movements, just sufficient for their 

 needs, their organization has gradually become adapted 

 to their new habits, and from this it will result : 



" I. That the arms of these animals making con- 

 tinual efforts readily to embrace the branches of trees, 

 would become elongated; 



" 2. That the nails of their digits would acquire 

 much length and a hooked shape, by the continued 

 efforts of the animal to retain its hold ; 



" 3. That their digits never having been trained to 

 make special movements, would lose all mobility 

 among themselves, would become united, and would 

 only preserve the power of bending or of straighten- 

 ing out all together; 



" 4. That their thighs, continually embracing both 

 the trunks and the larger branches of trees, would 

 contract a condition of habitual separation which 



