DARWIN: EMBRYOLOGICAL ARCHETYPE 237 



resembling each other of the structure of the embryo not 

 being closely related to its conditions of existence, except 

 when the embryo becomes at any period of life active and 

 has to provide for itself of the embryo apparently having 

 sometimes a higher organisation than the mature animal, into 

 which it is developed " (pp. 442-3). Obviously all these facts 

 are formally'explained by the doctrine of descent But Darwin 

 goes further, he tries to show exactly how it is that the 

 embryos resemble one another more than the adults. He 

 thinks that the phenomenon results from two principles- 

 first, that modifications usually supervene late in the life of 

 the individual ; and second, that such modifications tend to 

 be inherited by the offspring at a corresponding, not early, 



age (p. 444)- 



Thus, applying these principles to a hypothetical case of 

 the origin of new species of birds from a common stock, 

 he writes : " . . . from the many slight successive steps of 

 variation having supervened at a rather late age and 

 having been inherited at a corresponding age, the young 

 of the new species of our supposed genus will mani- 

 festly tend to resemble each other much more closely than 

 do the adults, just as we have seen in the case of pigeons" 



(PP- 446-7)- 



Since the embryo shows the generalised type, the struc- 

 ture of the embryo is useful for classificatory purposes. " For 

 the embryo is the animal in its less modified state ; and in 

 so far it reveals the structure of its progenitor" (p. 449) the 

 embryological archetype reveals the ancestral form. " Em- 

 bryology rises greatly in interest, when we thus look at the 

 embryo as a picture, more or less complete, of the parent 

 form of each great class of animals " (p. 450) a prophetic 

 remark, in view of the enormous subsequent development of 

 phylogenetic speculation. 



We may sum up by saying that Darwin interpreted von 

 Baer's law phylogenetically. 



The rest of the chapter is devoted to a discussion of 

 abortive and vestigial organs, whose existence Darwin 



1 In which nestlings of the different varieties are much more alike 

 than adults. Darwin attached much importance to this idea, see 

 Life and Letters, i., p. 88, and ii., p. 338, 



