Chap. XXVI. ANALOGOUS VARIATION. 343 



pigeons, and in the whole plumage of certain varieties of the duck. 

 Analogous facts in the vegetable kingdom could be given. 



Many sub-varieties of the pigeon have reversed and somewhat 

 lengthened feathers on the back part of their heads, and this is 

 certainly not due to reversion to the parent-species, which shows 

 no trace of such structure : but when we remember that sub-varie- 

 ties of the fowl, turkey, canary-bird, duck, and goose, all have either 

 topknots or reversed feathers on their heads ; and when we remember 

 that scarcely a single large natural group of birds can be named, in 

 which some members have not a tuft of feathers on their heads, we 

 may suspect that reversion to some extremely remote form has 

 come into action. 



Several breeds of the fowl have either spangled or pencilled 

 feathers; and these cannot be derived from the parent- species, the 

 Uullus hankiva ; though of course it is possible that one early pro- 

 genitor of this species may have been spangled, and another pen- 

 cilled. But, as many gallinaceous birds are either spangled or pen- 

 cilled, it is a more probable view that the several domestic breeds 

 of the fowl have acquired this kind of plumage from all the 

 members of the family inheriting a tendency to vary in a like 

 manner. The same principle may account for the ewes in certain 

 breeds of sheep being hornless, like the females of some other 

 hollow-horned ruminants ; it may account for certain domestic cats 

 having slightly-tufted ears, like those of the lynx ; and for the skulls 

 of domestic rabbits often differing from one another in the same 

 characters by which the skulls of the various sjDecies of the genus 

 Lepus differ. 



I will only allude to one other case, already discussed. Now 

 that we know that the wdld parent of the ass commonly has striped 

 legs, we may feel confident that the occasional appearance of stripes 

 on the legs of the domestic ass is due to reversion ; but this will not 

 account for the lower end of the shoulder-stripe being sometimes 

 angularly bent or slightly forked. So, again, when we seen dun 

 and other coloured horses with stripes on the spine, shoulders, and 

 legs, we are led, from reasons formerly given, to believe that they 

 reappear through reversion to the wild parent-horse. But when 

 horses have two or three shoulder- stripes, with one of them occa- 

 sionally forked at the lower end, or when they have stripes on their 

 faces, or are faintly striped as foals over nearly their whole bodies, 

 with the stripes angularly bent one under the other on the fore- 

 head, or irregularly branched in other parts, it would be rash to 

 attribute such diversified characters to the reappearance of those 

 proper to the aboriginal wild horse. As three African species of 

 the genus are much striped, and as we have seen that the crossing 

 of the unstriped species often leads to the hybrid offspring being 

 conspicuously striped — bearing also in mind that the act of crossing 

 certainly causes the reappearance of long-lost characters — it is 

 a more probable view that the above-specified stripes are due to 

 reversion, not to the inmaediate wild jjareut-horse, but to the stri])ed 

 progenitor of the whole genus. 



