12 



EARLY MAN IN BRITAIN. 



[CHAP. i. 



These facts appear to me inexplicable on any other theory 

 than that of evolution. 



LIVING SPECIES 

 ONE EXTINCT SPECIES 



LIVING SPECIES 



ABUNDANT 

 SEVERAL EXTINCT SPECIES 



SECONDARY PERIOD 



FIG. 1. Specialisation of Mammalia in Tertiary Period. 



No similar series of changes such as these has been 

 observed in the reptiles, amphibians, fishes, or in the 

 Invertebrates of the Tertiary strata, nor is it clearly 

 marked in the Tertiary vegetation. In the birds, how- 

 ever, a similar specialisation has been pointed out by Pro- 

 fessor Milne Edwards. The living orders, families, and 

 genera of the lower Vertebrates had already appeared in 

 the Primary and Secondary periods ; first, the lower and 

 afterwards the higher forms, preserving in their succes- 

 sive appearances the order in which they are arranged 

 in the classification of the naturalists. 



