THE DOGMA OF EVOLUTION 



tions are common to both sexes, or at least to the individuals 

 which produce the young.^° 



Lamarck, after formulating his laws on the changes 

 produced in structure and organs by use and disuse 

 and the indirect influence of the environment, gives 

 many examples to illustrate the laws. We need to in- 

 dicate only two to show the trend of his thought. 



Birds which have the habit of feeding on land 

 products may, by some change of conditions, have 

 their supply reduced. If they also live near a body of 

 water, they will endeavour to satisfy their need for 

 food by obtaining it from the water where it may be 

 abundant. Their efforts to reach this new kind of 

 food stimulate the nervous actions and the blood sup- 

 ply of those parts which aid in obtaining this food. 

 Some attempt to swim and strike the water with their 

 feet. The skin which unites the digits of their feet is 

 stretched and stimulated by this effort; thus, in course 

 of time, there are formed the webbed feet of ducks and 



10 Lamarck, op. cit., vol. I, p. 235 [p. 113]. Lamarck later, in his 

 Histoire naturelle des animaux sans vertebres divided these laws, 

 and made them rather more explicit. In this later form they are as 

 •follows : 



Premiere loi.— La vie, per ses propres forces, tend continuelle- 

 ment a accroitre le volume de tout corps qui la possede, et a etendre 

 les dimensions de ses parties, jusqu'a un terme qu'elle amene elle- 

 meme. 



Deuxieme loi. — La production d'un nouvel organe dans un corps 

 animal resulte d'un nouveau besoin survenue qui continue de se 

 faire sentir, et d'un nouveau mouvement que ce besoin fait naitre et 

 entretlent. 



Troisieme loi. — Le developpement des organes et leur force d'ac- 

 tion sont constamment en raison de I'emploi de ces organes. 



Quatrieme loi. — Tout ce qui a ete acquis, trace ou change dans 

 I'organisation des individus, pendant le cours de leur vie, est con- 

 serve par la generation et transmis aux nouveaux individus qui 

 proviennent de ceux qui ont eprouve ces changements. 



c 180 n 



