106 CHARLES DARWIN 



from Embryological Development, and the argument 

 from Classificatory Affinities. Each of these we may 

 briefly summarise. 



The geological record is confessedly imperfect. At 

 the time when Darwin first published the ' Origin of 

 Species,' it had disclosed to our view comparatively few 

 intermediate or transitional forms between the chief 

 great classes of plants or animals ; since that time, in 

 singular confirmation of the Darwinian hypothesis, it 

 has disclosed an immense number of such connecting 

 types, amongst which may be more particularly noticed 

 the ' missing links ' between the birds and reptiles, the 

 ancestors of the horses, the camels, and the pigs, and 

 the common progenitor of the ruminants and the 

 pachyderms, two great groups classed by Cuvier as 

 distinct orders all of which instances were incorporated 

 by Darwin in later editions of his ' Origin of Species.' 

 But, apart from these special and newly discovered cases, 

 the whole general course of geological history ' agrees 

 admirably with the theory of descent with modification 

 through variation and natural selection.' The simpler 

 animals of early times are followed by the more complex 

 and more specialised animals of later geological periods. 

 As each main group of animals appears upon the stage 

 of life, it appears in a very central and ' generalised ' 

 form; as time goes on, we find its various members 

 differing more and more widely from one another, and 

 assuming more and more specialised adaptive forms. 

 And in each country it is found, as a rule, that the 

 extinct animals of the later formations bear a close 

 general resemblance and relationship to the animals 

 which now inhabit the same regions. For example, 



