Embryology. 135 



Haeckel has been one of the most convinced and 

 luminous exponents of the idea of recapitulation, which 

 he called "das biogenetisches Grundgesetz ", and ex- 

 pressed in the now familiar words, "ontogeny tends to 

 recapitulate phylogeny". He also drew the distinction 

 between palingenetic characters, dating from the ancient 

 ancestral stock, and kainogenetic characters, regarded 

 as relatively recent adaptations. 



Such is, at least, part of the intellectual pedigree of 

 a theory which has had a profound influence on zoologi- 

 cal embryology, and in much wider inquiries, throughout 

 the Darwinian era. It seems to have found but little 

 acceptance among botanists. 



Of recent years there has been a strong reaction from 

 belief in the recapitulation doctrine, and the reasons for 

 this must be briefly considered. 



(a) Everyone, of course, resents the popular travesties 

 of the doctrine that have got afloat, e.g. that the human 

 embryo is at one stage like a little fish, later like a little 

 reptile, and so on ; but it will be admitted that even the 

 doctrine of evolution suffers similar violence, (b) Al- 

 though even an expert embryologist, such as Milnes 

 Marshall, may have said, " Every animal in its own 

 development repeats its history, climbs up its own 

 genealogical tree", we know that this was meant "in a 

 wide and metaphorical sense". As Haeckel has clearly 

 emphasized, the recapitulation asserted is general, not 

 exact, there is frequently a tendency to abbreviation, 

 and kainogenetic adaptations may disguise the palin- 

 genetic features. It hardly needs to be mentioned that 

 one term in the comparison, the phylogeny, is in most 

 cases very imperfectly known either from the actual 

 fossil records or from the inferences of the comparative 

 anatomists, (c) The recapitulation-theory was not in- 

 tended as a contribution to the physiology of develop- 

 ment, but rather as an historical interpretation. It is, 

 so to speak, a light from a distance, and does not touch 

 the question of the immediate conditions which lead on 

 from stage to stage. It is a fact that the frog ovum 

 gives origin to a larva with various fish-like structures 

 gill-slits, gills, two-chambered heart, &c.; it is a 



