68 SECTIONAL ADDRESSES 



and Brachiopods, Hyatt and Beecher were able to find the adult character- 

 istics of later types represented in the adolescent stages of earlier ones. 

 They found in the growth-stages of a single individual a succession of 

 characters that agreed with the palaeontological succession of its kindred. 

 R. T. Jackson applied the method of study to Pelecypods, and enlarged 

 the scope of the theory by his recognition of ' localised stages in develop- 

 ment ' in forms, such as Echinoderms and Plants, where early features are 

 modified or destroyed during life. 



Although the principle of perpetual recapitulation has stimulated a vast 

 bulk of palgeontological research, it has scarcely attracted among neon- 

 tologists the attention it deserves. Work along these lines on recent 

 material has generally been done by palaeontologists, for there still exists 

 a perverse tendency among neontologists to give but scant attention to 

 the hard parts of their victims. Especially does one note with regret 

 that developmental studies seem, for the most part, to stop when the 

 embryo is hatched, even if they extend beyond gastrulation. 



Just as a blind faith in the infallibility of embryological recapitulation 

 led to such absurdities that the whole principle was in danger of discredit, 

 so uncritical acceptance of Hyatt's principle of post-larval recapitulation 

 has at times been brought into disrepute. Especially has this occurred 

 when developmental stages were accepted as evidence of phylogenetic 

 descent without the precaution of checking the assumed succession by 

 field evidence. The order of occurrence, like the order of superposition 

 In stratigraphy, must always be the final test of any scheme based on other 

 evidence. It must be admitted that the formidable, and largely un- 

 necessary, terminology whose invention seems to have been a passion with 

 Hyatt, made unpalatable and obscure the facts that it was designed to 

 elucidate ; and also that some of the illustrations he used were un- 

 fortunately chosen. But no amount of criticism or scepticism can vitiate 

 the discoveries of Branco, Beecher and Carruthers ; the principle is sound 

 even if some of its exponents have been mistaken. 



Post-larval recapitulation, with its extension into senile prophecy, 

 provides a link between racial evolution and individual life. Most of 

 Hyatt's terminology was based on analogy with individual life ; the seven 

 ages of man became symbols of the stages of morphogeny and phylogeny. 

 In its fullest implications, it completes the tale of the uniformity of natural 

 laws working on different scales. Just as the history of a family is similar 

 to, but longer than, that of one of its component genera, and that of a 

 genus than that of one of its species, so the evolution of a species is shown 

 in an abbreviated and bowdlerised form in the life of one of its individual 

 members. Inception and extinction of species have their counterparts 

 in the birth and death of an organism, and the phases that intervene can 

 be matched in each case. It is usual, and proper, to speak of a genus or 

 species as representing an early or late stage in the evolution of its line ; 

 it is often possible to demonstrate that these terms have the same sort of 

 significance as the words young or old when applied to individuals. In 

 short, the delightfully simple conception emerges that the life of an 



