2o:i 



The Study of Atiinial Life part hi 



One must be careful not to press the idea of recapitulation 

 too far, (i) because the individual life-history tends to skip 



stages which occurred in the an- 

 cestral progress ; (2) because the 

 young animal may acquire new 

 characters which are peculiar to 

 its own near lineage and have 

 little or no importance in connec- 

 tion with the general evolution of 

 its race ; (3) because, in short, 

 the resemblance between the indi- 

 vidual and racial history (so far 

 as we know them) is general, not 

 precise. Thus we regard Nauplius 

 and Zoea rather as adaptive larval 

 forms than as representatives of 

 ancestral crustaceans. More- 

 over, if one insists too much on 

 the approximate parallelism be- 

 tween the life-history of the indi- 

 vidual and the progress of the 

 race, one is apt to overlook the 

 deeper problem- — how it is that 

 the recapitulation occurs to the 

 extent that it undoubtedly does. 

 The organism has no feeling for 

 history that it should tread a 

 sometimes circuitous path, be- 

 cause its far-off ancestors did so. 

 To some extent we may think of 

 inherited constitution as if it were 

 the hand of the past upon the 

 organism, compelling it to become 

 thus or thus, but we must realise 

 that this is a living not a dead 

 hand ; in other words these meta- 

 morphoses have their efficient causes in the actual con- 

 ditions of growth and development. The suggestion of 

 Kleinenberg referred to in a preceding chapter helps us, for 



