Lamarck:' s theory of evolution 245 



sidered in another organism which has not, or has 

 but slightly, exercised it. It is also very easy to prove 

 that the constant lack of exercise of an organ gradu- 

 ally reduces it and ends by atrophying it." 



Then follow the facts regarding the mole, spalax, 

 ant-eater, and the lack of teeth in birds, the origin of 

 shore birds, swimming birds and perching birds, which 

 are stated farther on. 



* Thus the efforts in any direction, maintained for 

 a long time or made habitually by certain parts of a 

 living body, to satisfy the needs called out \exig^s) by 

 nature or by circumstances, develop these parts and 

 cause them to acquire dimensions and a form which 

 they never would have obtain^^fcf these efforts had 

 not become an habitual action^w the animals which 

 have exercised them. Observations made on all the 

 animals known would furnish examples of this. 



" When the will determines an animal to any kind 

 of action, the organs whose function it is to execute 

 this action are then immediately provoked by the 

 flowing there of subtile fluids, which becorne the deter- 

 mining cause of movements which perform the action 

 in question. A multitude of observations support this 

 fact, which now no one would doubt. 



" It results from this that multiplied repetitions of 

 these acts of organization strengthen, extend, develop, 

 and even create the organs which afe there needed. It 

 is only necessary to closely observe that which is every- 

 where happening in this respect to firmly convince 

 ourselves of this cause of developments and organic . 

 changes. 



" However, each charvge acquired in an organ by 

 habitual use sufificient to have formed {op&i) it is 

 preserved by generation, if it is comrnon to the in- 

 dividuals which unite in the reproduction of their 



