220 THE CHAIN OF LIFE. 



back to predecessors in Eocene times, even more closely re- 

 sembling them than those supposed to be ancestors of the 

 horse resemble that animal. But the few species now living 

 have thus a vast surplusage of possible ancestors. Many 

 species and genera are dropped without any modern repre- 

 sentatives, so that the tendency has been to a gradual elimina- 

 tion of surplus types, until only a few isolated and somewhat 

 specialised forms remain at present. Yet this process of 

 elimination is not necessarily an evolution or survival of the 

 fittest, in the sense of modern derivationists. It rather implies 

 that in certain past conditions of the earth the conditions of 

 life afforded scope for many forms not now required, or 

 replaced by other types more suited to the advanced and 

 specialised nature of the world. 



On the other hand, the Artiodactyls have gained in numbers 

 and importance, in comparison with their odd-toed comrades ; 

 and this, though an odd number, namely five, was the typical 

 number with which the earliest quadrupedal forms began life 

 far back in the Palaeozoic. The typical Artiodactyls are those 

 that cleave the hoof, and many of which also chew the cud ; 

 and they are of all others, the horse perhaps excepted, those 

 that are most valuable to man. The lower type (Bunodont), 

 to which the hog belongs, is the older; and many hog-like 

 animals occur from the earlier Tertiary upwards. In the 

 Upper Eocene, even-toed species appear with an approach at 

 least to the crescent-shaped teeth of the modern deer and 

 oxen. Some of the species are obviously forerunners of the 

 modern antelopes and deer, though as yet destitute of horns or 

 antlers. Others, like Oreodon, are of more hog-like aspect, 

 though believed to have been ruminants (Fig. 177). These 

 are characteristic of the Middle Miocene, at which stage true 

 deer appear in Europe (Dicroceras), though they are not known 

 in America until the Pliocene period. The earliest deer have 

 small and simple antlers, these ornaments becoming larger 

 and more elaborate in approaching the modern era. The 



