The T heory 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 
E 
