202 MAMMALIAN DESCENT. [L.ECT. VIII. 



Professor Huxley on the Evolution of the Hm i se type. 



" Since the commencement of the Eocene 



epoch, the animals which constitute the family of the 

 Equidae have undergone processes of modification of 

 three kinds 



" 1. There has been an excess of development of some 

 parts in relation to others. 



" 2. Certain parts have undergone complete or partial 

 suppression. 



" 3. Certain parts, which were originally distinct, have 

 coalesced. 



" Employing the term ' law ' simply in the sense of a 

 general statement of facts ascertained by observation, I 

 shall speak of these three processes by which the 

 Eohifpus form has passed into Equus as the expression of 

 a threefold law of evolution " " On the Arrange- 

 ment of the Mammalia," Proc. Zool Soc., 1880, p. 649. 



