The Theory of Evolution 49 



different sort of principle from that involved in the theory 

 of descent; but as a matter of fact the historical evidence 

 makes it probable that similar types of architecture are 

 largely the result of imitation and tradition. Certain varia- 

 tions may have been added by each architect, but it is just 

 the similarity of type or plan that is generally supposed to 

 be the outcome of a common tradition. 



Fleischmann's attempt in the following chapter to belittle 

 Gegenbaur's theory of the origin of the five-fingered type of 

 hand from a fin, like that of a fish, need not detain us, since 

 this theory is obviously only a special application which like 

 any other may be wrong, without in the least injuring the 

 general principle of descent. That all phylogenetic questions 

 are hazardous and difficult is only too obvious to any one 

 familiar with the literature of the last thirty years. 



Fleischmann devotes a long chapter to the geological evi- 

 dences in connection with the evolution of the horse, and 

 attempts to throw ridicule on the conclusions of the paleon- 

 tologists by emphasizing the differences of opinion that have 

 been advanced in regard to the descent of this form. After 

 pointing out that the horse, and its few living relatives, the 

 ass and the zebra, are unique in the mammalian series in 

 possessing a single digit, he shows that by the discovery of 

 the fossil horses the group has been simply enlarged, and 

 now includes horses with one, three, and five toes. The 

 discovery of the fossil forms was interpreted by the advocates 

 of the descent theory as a demonstration of the theory. The 

 series was arranged by paleontologists so that the five-toed 

 form came first, then those with three and one toe, the 

 last represented by the living horses. But the matter was 

 not so simple, Fleischmann points out, as it appeared to 

 be to the earlier writers, for example to Haeckel, Huxley, 

 Leidy, Cope, Marsh. Different authors came to express 

 different opinions in regard to the genealogical connection 

 between the fossil forms. Several writers have tried to show 



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