THE RECAPITULATION THEORY 343 



But for the foldings of the surface the proportion of 

 white matter to grey matter would be far higher in 

 a large than in a small brain. 



It must not be forgotten on the other hand, that 

 many zoologists hold the view, in favour of which 

 the evidence is steadily increasing, that the primitive 

 or ancestral members of each group were of small 

 size. Thus Furbringer remarks with regard to 

 birds that on the whole small birds show more 

 primitive and simpler conditions of structure than 

 the larger members of the same group. He 

 expresses the opinion that the first birds were 

 probably smaller than Archaeapteryx, and notes that 

 reptiles and mammals also show in their earlier and 

 smaller types more primitive features than do their 

 larger descendants. Finally, Furbringer concludes 

 that "it is therefore the study of the smaller 

 members within given groups of animals which 

 promises the best results as to their phylogeny." 



Again, one of the most striking points with 

 regard to the pedigree of the horse, as agreed on 

 by palaeontologists, is the progressive reduction in 

 size which we meet with as we pass backwards in 

 time from stage to stage. The Pliocene Hipparion 

 was smaller than the existing horse, in fact about 

 the size of a donkey ; the Miocene Mesohippus 

 about equalled a sheep ; while Eohippus, from the 

 Lower Eocene deposits, was no larger than a fox. 

 Not only is there good reason for holding that as 

 a rule larger animals are descended from ancestors 

 of smaller size, but there is also much evidence to 

 show that increase in size beyond certain limits is 



