WITHIN THE EGG 181 



that ontogeny recapitulates phylogeny, that the developing 

 creature climbs up its own genealogical tree, has been of 

 service, but it has also been mischievous. It is so easily 

 exaggerated. Till the sixth day in the case of the chick the 

 embryo is not visibly a bird embryo ; it might be a reptile 

 embryo as far as external inspection tells us ; but it is never 

 like a fish, nor ever like any reptile, it is only like an embryo- 

 fish, an embryo-reptile. The recapitulation is rather in the 

 development of organs than in the development of the 

 embryo as a whole. The appearance and disappearance of 

 the notochord, the gill-clefts, and the visceral arches, the 

 stages in the development of heart and circulation, the brain 

 and the skull, are wonderfully like recapitulations, and we do 

 not know how any one could interpret the appearance and 

 rapid disappearance of old-fashioned organs like the noto- 

 chord and the gill-clefts except as vestigial relics of long- past 

 racial history. But it must be emphasised that the so-called 

 recapitulation is a very general one : that it is seen rather in 

 the stages of organs than in the phases of the whole creature ; 

 that it is a recapitulation of embryonic stages, not of adult 

 forms ; that it is often condensed and, as it were, telescoped ; 

 and that in very early days there are evidences of the 

 specific bird that is to be. 



Embryology is entirely a modern science. Though 

 Aristotle (384-322 B.C.) watched the heart -beats of the still 

 unrecognisable chick within the egg, and had hold of the idea 

 that development is a progressive differentiation, he had 

 practically no successors before Harvey (1578-1657). 



Harvey got a grip of the fact that almost every living 

 creature is produced from an egg ovum esse primordium 

 commune omnibus animalibus and of the fact that the 

 initial stage is not a preformed model, but something 

 apparently simple, in which, as he said, " no part of the 

 future organism exists de facto, but all parts inhere in 



