CHAP. V.] ANALOGOUS VARIATIONS. 121 



to Mr. Gosse, in certain parts of the United States about nine out 

 of ten mules have striped legs. I once saw a mule with its legs 

 so much striped that any one might have thought that it was a 

 hybrid-zebra ; and Mr. W. C. Martin, in his excellent treatise on 

 the horse, has given a figure of a similar mule. In four coloured 

 drawings, which I have seen, of hybrids between the ass and 

 zebra, the legs were much more plainly barred than the rest of 

 the body ; and in one of them there was a double shoulder-stripe. 

 In Lord Morton's famous hybrid, from a chestnut mare and male 

 quagga, the hybrid, and even the pure offspring subsequently pro- 

 duced from the same mare by a black Arabian sire, were much 

 more plainly barred across the legs than is even the pure quagga. 

 Lastly, and this is another most remarkable case, a hybrid has 

 been figured by Dr. Gray (and he informs me that he knows of a 

 second case) from the ass and the hemionus; and this hybrid, 

 though the ass only occasionally has stripes on his legs and the 

 hemionus has none and has not even a shoulder-stripe, nevertheless 

 had all four legs barred, and had three short shoulder-stripes, like 

 those on the dun Devonshire and Welsh ponies, and even had 

 some zebra-like stripes on the sides of its face. With respect to 

 this last fact, I was so convinced that not even a stripe of colour 

 appears from what is commonly called chance, that I was led 

 solely from the occurrence of the face-stripes on this hybrid from 

 the ass and hemionus to ask Colonel Poole whether such face- 

 stripes ever occurred in the eminently striped Kattywar breed of 

 horses, and was, as we have seen, answered in the affirmative. 



What now are we to say to these several facts 1 We see several 

 distinct species of the horse-genus becoming, by simple variation, 

 striped on the legs like a zebra, or striped on the shoulders like 

 an ass. In the horse we see this tendency strong whenever a 

 dun tint appears a tint which approaches to that of the general 

 colouring of the other species of the genus. The appearance of 

 the stripes is not accompanied by any change of form or by any 

 other new character. We see this tendency to become striped 

 most strongly displayed in hybrids from between several of the 

 most distinct species. Now observe the case of the several breeds 

 of pigeons : they are descended from a pigeon (including two or 

 three sub-species or geographical races) of a bluish colour, with 

 certain bars and other marks ; and when any breed assumes by 

 simple variation a bluish tint, these bars and other marks invari- 

 ably reappear ; but without any other change of form or character. 

 When the oldest and truest breeds of various colours are crossed, 

 we see a strong tendency for the blue tint and bars and marks to 

 reappear in the mongrels. I have stated that the most probable 

 hypothesis to account for the reappearance of very ancient cha- 

 racters, is that there is a tendency in the young of each succes- 



