I A CHAPTER IN DARWINISM 43 



occurs that the most important 'part of the recapitula- 

 tive phases are absent from the developmental history 

 of an animal. The egg proceeds very rapidly to pro- 

 duce the adult form, and all the wonderful series of 

 changes showing the animal's ancestry are absolutely 

 and completely omitted ; that is to say, all those stages 

 which are of importance for our present purpose. Just 

 as certain bodies pass from the solid to the liquid state 

 at a bound, omitting all intermediate phases of con- 

 sistence, but giving evidence of "internal work" by 

 the suggestive phenomenon of latent heat — so do these 

 embryos skip long tracts in the historically continuous 

 phases of form, and present to us only the intangible 

 correlative " internal work " in place of the tangible 

 series of embryonic changes of shape. 



Now I want to put this case — a supposition — before 

 the reader who has so far followed me in these pages. 

 Suppose, as might well have happened, that the Bar- 

 nacles, one and all, instead of recapitulating in their 

 early life, were to develop directly from the egg to the 

 adult form, as so many animals do ; should we have 

 ever made out that they were degenerate Crustaceans ? 

 Possibly we should : their adult structure still bears 

 important marks of affinities with crabs and shrimps ; 

 but as a matter of fact before their recapitulative de- 

 velopment had been discovered they were classed by 

 the great Cuvier and other naturalists with the jMolluscs, 

 the mussels and snails. 



Suppose again that all the existing Ascidians, as 

 many of them actually have, had long ago lost their 

 recapitulative history in growth from the egg : suppose 



