112 ORGANIC EVOLUTION CONSIDERED 



more to less generalized types, within the limits of 

 the period represented by the fossiliferous rocks?' I 

 reply, ' It negatives these doctrines ; for it either 

 shows us no evidence of such modifications, or demon- 

 strates such modification as has occurred to have 

 been very slight ; and as to the nature of that modi- 

 fication, it yields no evidence whatsoever that the 

 earlier members of any long-continued group were 

 more generalized in structure than the latter ones. 



" The significance of persistent types and of the 

 small amount of change which has taken place even 

 in those forms which can be shown to have been mod- 

 ified, becomes greater and greater in my eyes, the 

 longer I occupy myself with the biology of the past. 



" Consider how long a time has elapsed since the 

 Miocene epoch. Yet, at that time there is reason to 

 believe that every important group in every important 

 order of the Mammalia was represented. Even the 

 comparatively scanty Eocene fauna yields examples 

 of the orders Cheiroptera, Insectivora, Eodentia and 

 Perissodactyla; of Artiodactyla under both the 

 Ruminant and the Porcine modifications; of Car- 

 nivora, Cetacea and Marsupialia. 



" Or, if we go back to the older half of the Meso- 

 zoic epoch, how truly surprising it is to find every 

 order of the Reptilia, except the Ophidia, repre- 

 sented; while some groups, such as the Ornithoscelida 

 and the Pterosauria, more specialized than any which 

 now exist, abounded." 



He then speaks of the Labyrinthodonts which 

 extend " from the bottom of the Carboniferous series 

 to the top of the Trias, if not into the Lias." And 

 continues, " Since that time eight or ten distinct 

 genera of Labyrinthodonts have been discovered in 

 the Carboniferous rocks of England, Scotland and 

 Ireland, not to mention the American forms described 



