340 THE RECAPITULATION THEORY 



be, and probably is, a general parallelism between 

 the increase in size from the egg to the adult, and 

 the historical increase in size during the passage 

 from lower to higher forms ; yet no one could 

 maintain that the sizes of embryos represent at all 

 correctly those of the ancestors ; that for instance 

 the earliest birds were animals the size of a chick 

 embryo at a time when avian characters first declare 

 themselves, or that the ancestral series in all cases 

 presented a steady progression in respect of actual 

 magnitude. 



In the lower animals e.g., in Orbitolites the 

 actual size of the several ancestral stages is probably 

 correctly recapitulated during the growth of the 

 adult ; and it is very possible that it is so also in 

 such forms as the solitary sponges. In higher 

 animals, except in the early stages of those forms 

 which are practically devoid of food yolk, and which 

 hatch as pelagic larvae, this certainly does not 

 obtain. This is clear enough, but is worth point- 

 ing out, for if as most certainly is the case the 

 embryos of animals are actually smaller than the 

 ancestral forms they represent, it is possible that 

 the smallness of the embryo may have had some 

 influence on its organisation, and be responsible 

 for some of the modifications in the ances- 

 tral history ; and more especially for the disap- 

 pearance of ancestral organs in free swimming 

 larvae. 



In adult animals the relation between size and 

 structure has been very clearly pointed out by 

 Herbert Spencer. Increased size involves by itself 



