INDIRECT EVIDENCE. 49 



the horse and the ass are crossed, the offspring pos- 

 sesses features which are found in neither parent. 

 The mule, in ninety cases out of a hundred, shows a 

 number of bars on the legs, and several stripes on the 

 shoulders. In rare instances it is found that the 

 horse and ass of pure breed possess the same feat- 

 ures, scattered cases having been observed in almost 

 every variety of horse and ass. But hybrids almost 

 always show them. Not only the hybrid between 

 the horse and the ass, but all hybrids of the various 

 members of the horse family, show the same features. 

 The similarity of this case with that of the pigeons 

 is exact, and plainly indicates that here is a true case 

 of reversion. Now in the pigeons it is known that 

 the reversions refer to a common ancestor of the 

 breeds crossed. It is certainly a legitimate inference 

 that the reversions occurring in the horse family also 

 refer to a common ancestor. When, therefore, we 

 find various species of the horse family, the horse, 

 the ass, the zebra, the quagga, the hemionus, all 

 showing this tendency to reversion, we can hardly 

 avoid the conclusion that they have had a common 

 ancestor. Our naturalists have even thought it pos- 

 sible to tell pretty accurately the specific features of 

 this ancestor of the horse family, drawing their con- 

 clusions from these reversions, together with other 

 evidence. The common ancestor of the horse family, 

 they tell us, was an animal somewhat smaller than the 

 ass, of a dun color, and with stripes much like those of 

 the zebra. If this evidence is accepted, it is plain 

 that the common origin of some species is no longer 

 a matter of question. It is of course possible to 



