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 are 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- 



