50 Evolution and Adaptation 
that the present genus, Equus, has not had a single line of 
descent, but have supposed that the European horses and 
the original American horses had different lines of ancestry, 
which may have united only far back in the genus Epihippus. 
Fleischmann points out that the arrangement of the series 
is open to the criticism that it is arbitrary, and that we could 
equally well make up an analogous series beginning with the 
five-fingered hand of man, then that of the dog with the 
thumb incompletely developed, then the four-fingered hind- 
foot of the pig without a big toe and with a weak second and 
fifth digit, then the foot of the camel with only two toes, 
and lastly the foot of the horse with only one toe. It sounds 
strange that Fleischmann should make such a trivial reply as 
this, and deliberately ignore the all-important evidence with 
which he is, of course, as is every zoologist, perfectly con- 
versant. Not only afe there a hundred other points of 
agreement in the horse series, but also the geological 
sequence of the strata, in which some at least of the series 
have been found, shows that the arrangement is not arbitrary, 
as he implies. 
Fleischmann then proceeds to point out that when the 
evidence from other parts of the anatomy is taken into 
account, it becomes evident that all the known fossil re- 
mains of horses cannot be arranged in a single line, but 
that there are at least three families or groups recognizable. 
Many of these forms are known only from fragments of their 
skeletons —a few teeth, for instance, in the case of Mero- 
hippus, which on this evidence alone has been placed at 
the uniting point of two series. At present about eight dif- 
ferent species of living horses are recognized by zoologists, 
and paleontological evidence shows only that many other 
species have been in existence, and that even three- and one- 
toed forms lived together at the same time. 
Fleischmann also enters a protest against the ordinary 
arrangement of the fossil genera Eo-, Oro-, Meso-, Mero- 
