72 THE TRANSFORMATIONS OF THE ANIMAL WORLD 



taken as a whole, we shall have to be content with 

 the evidence supplied by certain particular groups ; 

 for example, the Mammalia, the Ammonites, and the 

 Echinida, which give us either relatively short 

 series of continuous forms, or more extended series, 

 only a few of the links of which are connected by 

 gradual transitions, but of which the whole is 

 modified in the same direction. These intermittent 

 series show us the road by which the animals of 

 early times have accomplished their evolution 

 towards the types of existing nature. 



As an example in support of his theoretical ideas, 

 J^eumayr takes the classic series of the ancestral 

 line of the Horse. This animal, from the point of 

 view of the reduction in the number of digits, 

 which comes down to one (the third) accompanied 

 by two bony splints which are the rudiments of 

 the fourth and fifth digits represents the extreme 

 term of a series of which the primitive types must 

 have had five digits, as in all the other higher Verte- 

 brates . In the Tertiary we have long been acquainted 

 with a certain number of animals which enable us to 

 follow step by step the successive stages of this reduc- 

 tion in the number of digits. There is the Palceo- 

 therium, with its three toes nearly equal and resting 

 on the ground ; the Anchitherium, with its highly 

 developed median toe and its two reduced lateral 

 toes no longer resting on the ground ; and by a still 

 more marked reduction of the lateral toes, the 

 Hipparion brings us down to the existing Horse. 

 These modifications of the foot are correlated to 

 other modifications of the hinder limb, of the den- 

 tition, and of the form of the skull. More recently 



