10 ADDRESS TO THE BRITISH ASSOCIATION, 1881. 



next year two points, in the following three, and so on ; 

 so the genus, as a whole, in Middle Miocene times, had 

 two pronged horns ; in the Upper Miocene, three ; and 

 that it is not till the Upper Pliocene that we find any 

 species with the magnificent antlers of our modern deer. 

 It seems to be now generally admitted that birds have 

 come down to us through the Dinosaurians, and, as 

 Huxley has shown, the profound break once supposed 

 to exist between birds and reptiles has been bridged 

 over by the discovery of reptilian birds and bird-like 

 reptiles ; so that, in fact, birds are modified reptiles. The 

 remarkable genus Peripatus, so well studied by Moseley, 

 tends to connect the annulose and articulate types. 



Again, the structural resemblances between Am- 

 phioxus and the Ascidians had been pointed out by 

 Goodsir ; and Kowalevsky in 1866 showed that these 

 were not mere analogies, but indicated a real affinity. 

 These observations, in the words of Allen Thomson, 

 ' have produced a change little short of revolutionary in 

 embryological and zoological views, leading as they do 

 to the support of the hypothesis that the Ascidian is an 

 earlier stage in the phylogenetic history of the mammal 

 and other vertebrates.' 



The larval forms which occur in so many groups, 

 and of which the Insects afford us the most familiar ex- 

 amples, are, in the words of Quatrefages, embryos, which 

 lead an independent life. In such cases as these, external 

 conditions act upon the Iarva3 as they do upon the 

 mature form ; hence we have two classes of changes, 

 adaptational or adaptive, and developmental. These 

 and many other facts must be taken into consideration ; 

 nevertheless naturalists are now generally agreed that 



