CKAP. v.] analogous variations. 127 



sively due to analogous variation would probably be of an unim- 

 portant nature, for the preservation of all functionally important 

 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 occa- 

 sionally exhibit reversions 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 variations ; but we might have inferred that the blue 

 colour was a case of reversion from the number of the markings, 

 which are correlated with this tint, and which would not probably 

 have all appeared together from simple variation. More especially 

 we might have inferred this, from the blue colour and the several 

 marks so often appearing when differently coloured 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 offspring of a species assuming- 

 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 bo 

 ranked as species ; and this shows, unless all these closely allied 

 forms be considered as independently created species, that they 

 have in varying 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 occa- 

 sionally 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 cer- 

 tainly occur, and seem to jae very remarkable. 



I will, however, give one curious and complex case, not indeed as 

 affecting any important character, but from occurring in several 

 species of the same genus, partly under domestication and partly 

 under nature. It is a case almost certainly of reversion. The asa- 

 sometimes has very distinct transverse bars on its legs, like those 

 on the legs of the zebra : it has been asserted that these are plainest 



