302 THE RECAPITULATION THEORY 



known researches* have shown that in the Ammon- 

 ites such a correspondence between historic and 

 embryonic development does really exist ; that, 

 for example, in Aspidoceras the shape and mark- 

 ings of the shells in young specimens differ greatly 

 from those of adults, and that the characters of the 

 young shells are those of palaeontologically older 

 forms. Another striking illustration of the cor- 

 respondence between palaeontological and develop- 

 mental records is afforded by the antlers of deer, 

 in which the gradually increasing complication of 

 the antler in successive years agrees singularly 

 closely with the progressive increase in size and 

 complexity shown by the fossil series from the 

 Miocene age to recent times. 



Of cases where a single specimen has sufficed to 

 prove the palaeontological significance of a develop- 

 mental character, Archaeopteryx affords a typical 

 example. In recent birds the metacarpals are 

 firmly fused with one another, and with the distal 

 series of carpals ; but in development the meta- 

 carpals are at first, and for some time, distinct. 

 In Archaeopteryx this distinctness is retained in 

 the adult, showing that what is now an embryonic 

 character in recent birds, was formerly an adult 

 one.f Other examples might easily be quoted, but 

 these will suffice to show that the relation between 



.Palaeontology and Embryology, first enunciated by 

 Agassiz, and required by the Recapitulation 



* L. WUrtenberger, " Studien iiber die Stammesgeschichte der 

 Ammoniten. Ein geologischer Beweis fur die Darwin 'sche 

 Theorie." Leipzig, 1880. 



