i.j THE QUEST OF A CRITERION 59 



the second which serves the usual practice of science, but 

 it is the first that generally provides its philosophy. In 

 any particular case one talks as if the process of adaptation 

 were an effort of the organism to build up a machine 

 capable of turning external circumstances to the best 

 possible account : then one speaks of adaptation in general 

 as if it were the very impress of circumstances, passively 

 received by an indifferent matter. 



But let us come to the examples. It would be interest- 

 ing first to institute here a general comparison between 

 plants and animals. One cannot fail to be struck with the 

 parallel progress which has been accomplished, on both 

 sides, in the direction of sexuality. Not only is fecunda- 

 tion itself the same in higher plants and in animals, since 

 it consists, in both, in the union of two nuclei that differ 

 in their properties and structure before their union and 

 immediately after become equivalent to each other; but 

 the preparation of sexual elements goes on in both under 

 like conditions : it consists essentially in the reduction of the 

 number of chromosomes and the rejection of a certain 

 quantity of chromatic substance. 1 Yet vegetables and 

 animals have evolved on independent lines, favored by 

 unlike circumstances, opposed by unlike obstacles. Here 

 are two great series which have gone on diverging. On 

 either line, thousands and thousands of causes have com- 

 bined to determine the morphological and functional 

 evolution. Yet these infinitely complicated causes have 

 been consummated, in each series, in the same effect. And 

 this effect could hardly be called a phenomenon of "adapt- 

 ation": where is the adaptation, where is the pressure 

 of external circumstances? There is no striking utility 



1 P. Gue'rin, Les Connaissances actuelles sur la ftcondation chez les 

 phanerogames, Paris, 1904, pp. 144-148. Cf. Delage, L'H&riditS, 

 2nd edition, 1903, pp. 140 ff. 



