C|HAPTER VII 

 THE DEVELOPMENT OF ORGANISMS 



{Embryological) 



INTRODUCTORY.— From the strange evolutionary history of 

 words, it is here well to recall that evolutio was first used to express 

 a theory no evolutionist now in that sense holds, a quaint sort of 

 germ-theory inverted, of the unfolding of the egg, regarded as an 

 already formed miniature of the adult. To meet criticism it was 

 added that the pre-formed miniature must contain in its germ an 

 ultra-miniature, and so on; like a nest of Chinese boxes being 

 unpacked since the creation. Modern embryology, since Harvey, has 

 on the contrary been following up what he called epigenesis, the 

 process which Von Baer, its modern re-initiator, formulated in the 

 law on which Herbert Spencer so largely built his philosophy, that 

 "the progress of development goes from the general to the special". 

 But beyond this conception, now so concretely verified throughout 

 living Nature, further general ideas have long since arisen; as 

 notably "the biogenetic law" which Haeckel so especially empha- 

 sised, and so boldly applied, that ontogeny repeats the course of 

 phylogeny, i.e. that the phases of development of the individual 

 are essentially recapitulations of the history of its race. Hence 

 Haeckel's Gastraea theory, for him a central clue throughout long- 

 ascending series: or again his emphasis on the Nauplius larva as 

 ancestral for the protean crustaceans, or again his comparisons of 

 similar embryos throughout the Vertebrate series from fish to man. 

 There was much truth in all this; a tadpole does in some measure 

 represent a gill-breathing and fishy ancestor, and then a lunged 

 fish, till it has lungs alone. But his sketchings were too bold; hence 

 a reaction followed, to embryological work in far more accurate 

 detail, and with many corrections of his outlines accordingly. Still, 

 it is now only fair to him to recall that he had so far anticipated 

 these: for beside his basal recapitulatory principle of "palingenesis", 

 and its frequent abbreviation in many forms towards more and more 

 direct development, he was, of course, not blind to the extra- 

 ordinary modification of larval and yet more of pupal life in insects, 

 for the latter phase especially cannot be imagined as an ancestral 

 one. The vast bulk of evidence points to the now so frequent larval 

 stage as an acquired byway, in course of ascent from primitive 

 insects with no metamorphoses at all. Kindred phenomena appear 

 in not a few other developments; so while Haeckel went too fast 



