CnAi-. V. HIGHLY VARIABLE. I.53 



different species beinp^ sometimes wlioUy unlike in shape; and 

 the amount of variation in the individuals of the same speciey 

 is so great, that it is no exaf^goration to state that the varieties 

 differ more from each other in the characters derived from these 

 important valves than do other species belonging to distinct 

 genera. 



As birds within the same country vary in a remarkably 

 small degree, I have jiarticuhu-ly attended to them, and the 

 rule seems to me certainly to hold good in this class. I cannot 

 make out that it applies to plants, and this would seriously 

 have shaken my belief in its truth, had not the great variability 

 in plants mad(; it jiarticularly dillicult to compare their relative 

 degrees of variabilit}'. 



When we see any part or organ developed in a remarkable 

 degree or maimer in any species, the fair presumption is, that 

 it is of high importance to that species ; nevertheless it is in 

 this case eminently liable to variation. Why should this be 

 so ? On the view that each species has been independently 

 created, with all its ])arts as we now see them, I can see no 

 explanation. But on the view that groups of species have 

 descended from other species, and have been modified through 

 natural selection, T think we can obtain some light. First, let 

 me remark that if any part in our domestic animals, or the 

 whole animal, be neglected and no selection be applied, that 

 I)art (for instance, the comb in the Dorking fowl) or the whole 

 bref'd will cease to have a imiforin character. The breed will 

 then be said to have degenerated. In rudimentary organs, and 

 in tijose which have been but little specialized for an}'' partic- 

 ular purpose, and perhaps in poljmiorphic groups, we see a 

 nearly parallel natural case; for in such cases natural selection 

 either has not or cannot have come into full play, and thus the 

 organization is left in a fluctuating condition. But what here 

 concerns us is, that those points in our domestic animals, whicli 

 at the present time are undergoing rapid change by continued 

 selection, are also eminently liable to variation. Look at the 

 breeds of the pigeon ; see what a prodigious amount of differ- 

 ence there is in tht; beaks of tumblers, in the beaks and wattle 

 of carriers, in the carriage and tail of fantails, etc., these being 

 the points now mainly attiMided to by Englisli fanciers. Even 

 in sub-breeds, as in that of the short-faced tumbler, it is notori- 

 ously dillicult to breed nearly perfect birds, some fre(|uently 

 departing widely from the standard. There may truly be said 

 to be a constant struggle going on between, on the one hand, 



