180 THE PATH OF DEGENERATIVE EVOLUTION 



of this principle to every individual case. Such an 

 exact application is, however, impossible. Every 

 living organism is plastic, and in its development 

 presents individual variations which serve as 

 material for the operation of natural selection. 

 In consequence, the recapitulation cannot be more 

 than a repetition more or less vague of the essential 

 phases of phylogeny. 1 



Moreover, there is nothing inevitable in the law 

 of recapitulation, for most plants develop directly. 



With these limitations, however, we may state 

 that among animals, the ontogeny usually repeats 

 in a modified fashion the main ancestral stages. 

 This is certainly the case when we compare the 

 development of the brain of man with the probable 

 ancestral stages as displayed in the series of verte- 

 brates. 



1 Lang, Anatomic compared. As throughout the whole course of 

 time, adaptation, that is to say, the preservation of what is most 

 useful in the struggle for existence, is a force modifying heredity, 

 it is plain that a species instead of resting stable must change. 

 According to its circumstances, moreover, the successive stages in 

 the ontogeny of a creature are under the influence of conditions 

 different from those that affected the corresponding ancestral stages. 

 We shall call the process of embryology palingenetic so far as it is 

 based upon inherited legacies, and coenogenetic so far as it is modi- 

 fied by adaptation. 



Baldwin in his Treatise on Mental development in the child and 

 in the race (London, 1895), also shows that the development of the 

 individual is not an exact repetition of ancestral stages. The 

 development of the child exhibits "short cuts" and phases of 

 direct development due to adaptation and destroying the exactness 

 of the parallel with phylogeny. 



