98 DOCTRINE OF EVOLUTION 



possessing hoofs, provide the same kind of conclusive 

 evidence. The feature of particular interest in the 

 case of their horns, is a correspondence between the 

 fossil sequence and the order of events in the life-history 

 of existing species, — that is, between the results of 

 palaeontology and of embryology. Horns of the 

 earliest known fossil deer have only two prongs ; in 

 the rocks above are remains of deer with additional 

 prongs, and point after point is added as the ancient 

 history of deer is traced upwards through the rocks to 

 modern species. We know that the life-history of 

 a modern species of animals reviews the ancestral 

 record of the species, ^and what happens during the 

 development of deer can be directly compared with 

 the fossil series. It is a matter of common knowledge 

 that the year-old stag has simple spikes as horns, and 

 that these are shed to be replaced the following year 

 by larger forked horns. Every year the horns are lost 

 and new ones grow out, and become more and more 

 elaborately branched as time goes on, thus giving a 

 series of developmental stages that faithfully repeats 

 the general order of fossil horns. Even Agassiz,who 

 was a believer in special creation and an opponent 

 of evolution, was constrained to point out many other 

 instances, mainly among the invertebrata, where there 

 was a like correspondence between the ontogeny of 

 existing species and their phylogenetic history as 

 revealed by the fossil remains of their ancestors. 



In the last place, we must give more than a passing 

 consideration to some of the extinct types of animals 



