ANALOGOtra VARIATIONS. 151 



due to analogous variation would probably be of an unim- 

 portant nature, for the preservation of all functionally im- 

 portant characters will have been determined through 

 natural selection, in accordance with the different habits 

 of the species. It might further be expected that the 

 species of the same genus would occasionally exhibit rever- 

 sions to long-lost characters. As, however, we do not 

 know the common ancestor of any natural group, we 

 cannot distinguish between reversionary and analogous 

 characters. If, for instance, we did not know that the 

 parent rock-pigeon was not feather-footed or turn-crowned, 

 we could not have told, whether such characters in our 

 domestic breeds were reversions or only analogous varia- 

 tions; but we might have inferred that the blue color was 

 a case of reversion from the number of the markings, 

 which are correlated with this tint, and which would not 

 probaby have all appeared together from simple variation. 

 More especially we might have inferred this from the blue 

 color and the several marks so often appearing when dif- 

 ferently colored breeds are crossed. Hence, although under 

 nature it must generally be left doubtful, what cases are 

 reversions to formerly existing characters, and what are 

 new but analogous variations, yet we ought, on our theory, 

 sometimes to find the varying ofEsjiriug of b species assum- 

 ing characters which are already present in other members 

 of the same group. And this undoubtedly is the case. 



The difficulty in distinguishing variable species is largely 

 due to the varieties mocking, as it were, other species of 

 the same genus. A considerable catalogue, also, could be 

 given of forms intermediate between two other forms, 

 which themselves can only doubtfully be ranked as species; 

 and this shows, unless all these closely allied forms be con- 

 sidered as independently created species, that they have in 

 varing assumed some of the characters of the others. But 

 the best evidence of analogous variations is afforded by 

 parts or organs which are generally constant in character, 

 but which occasionally vary so as to resemble, in some 

 degree, the same part or organ in an allied species. I have 

 collected a long list of such cases; but here, as before, I lie 

 under the great disadvantage of not being able to give 

 them. I can only repeat that such cases certainly occur, 

 and seem to me very remarkable. 



