ELEMENTARY VITAL PHENOMENA 



185 



Phyletic adaptation, i.e., the gradual adaptation of the series of 

 forms to existing vital conditions, has a disproportionate^ great, 

 perhaps a determinative, significance in the form-changes of 

 phylogenetic development. It takes place in a manner wholly 

 different from that of individual adaptation. Darwin's immortal 

 work ('59) consists in explaining naturally the surprising 

 purposefulness in the organic world by revealing the mode of 

 phyletic adaptation. According to Darwin's theory of selection 

 the adaptation of organisms to external conditions takes place, not 

 by the immediate change of the single individual, but by natural 



6 



FIG. 66. Amceba Umax, a, Contracted ; I, at the beginning of the formation of pseudopodia, 

 (proteus-foYTa) ; c, common Umax-form ; d, e,f, forms assumed after the addition of potash 

 solution ; d, at the beginning of the action ; e, /, radiosa-forms. 



selection among many individuals in the same manner as in the 

 improvement of the race by artificial selection on the part of the 

 breeder. 



Starting from the fact of individual variability, i.e., the pheno- 

 menon that in every generation of offspring from the same 

 parents no single individual is wholly like another, although to 

 ordinary observation the differences frequently appear very small, 

 Darwin finds as a necessary consequence of the struggle for 

 existence a choice, a selection, among the different individuals of 

 every generation according to the measure of their vital power. 

 It is known that in all organisms without exception more offspring 



