PRESIDENTIAL ADDRESS. 9 



in succession. If, therefore, tne development of the shell is a 

 repetition of ancestral history, the central chamber should 

 represent the palaeontologically oldest form, and the remaining 

 chambers in succession forms of more and more recent origin. 

 Ammonite shells present, more especially in their sutures, and in the 

 markings and sculpturing of their surface, characters that are easily 

 recognised, and readily preserved in fossils ; and the group, con- 

 sequently, is a very suitable one for investigation from this standpoint. 



"Wurtenberg's admirable and well-known researches 1 have shown that 

 in the Ammonites such a correspondence between the historic and 

 embryonic development does really exist ; that, for example, in 

 Aspidoceras the shape and markings of the shells irj 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 correspondence between the 

 palaeontological and developmental 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 developmental 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 metacarpals 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. 



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 Theory, 

 does in reality exist. There is much yet to be done in this direction. 

 A commencement, a most promising commencement, has been made, 

 but as yet only a few groups have been seriously studied from this 

 standpoint. 



It is a great misfortune that palaeontology is not more generally 



1 L. Wiirtenberger, ' Studien uber die Stammesgescliichte der Ammoniten. 

 Ein geologischer Beweis fur die Darwin'sche Theorie.' Leipzig, 1880. 



