Ill LECTURES ON EVOLUTION 115 



It is obviously useless to seek for such evidence 

 except in localities in which the physical condi- 

 tions have been such as to permit of the deposit 

 of an unbroken, or but rarely interrupted, series of 

 strata through a long period of time ; in which the 

 group of animals to be investigated has existed in. 

 such abundance as to furnish the requisite supply 

 of remains ; and in which, finally, the materials 

 composing the strata are such as to ensure the 

 preservation of these remains in a tolerably per- 

 fect and undisturbed state. 



It so happens that the case which, at present, 

 most nearly fulfils all these conditions is that of 

 the series of extinct animals which culminates in 

 the horses ; by which term I mean to denote not 

 merely the domestic animals with which we are all 

 so well acquainted, but their allies, the ass, zebra, 

 quagga, and the like. In short, I use " horses " 

 as the equivalent of the technical name Equidce, 

 which is applied to the whole group of existing 

 equine animals. 



The horse is in many ways a remarkable 

 animal ; not least so in the fact that it presents 

 us with an example of one of the most perfect 

 pieces of machinery in the living world. In truth, 

 among the works of human ingenuity it cannot be 

 said that there is any locomotive so perfectly 

 adapted to its purposes, doing so much work with 

 so small a quantity of fuel, as this machine of 

 nature's manufacture the horse. And, as a neces- 



