The True- Lime Group. 85 



Montserrat. Judging from its flowers, spines, and 

 form of leaflet, it appears to be related to the series 

 with large-winded petioles, and, perhaps, the reason 

 why I have invariably found the true lime with a winged 

 petiole, though generally small, may possibly be its 

 descent from one with a much larger winged petiole. 



Some might say, if so, why do we never find any 

 reversion in the lime to its ancestral large winged 

 petiole ? Perhaps this objection might be answered 

 better by a series of questions, (a) If it is, as botanists 

 say, that the true lime is a variety of Citrus medica, 

 why does it never revert to the petioles and leaves of 

 the citron, which are so different ? (&) Why does man's 

 internal tail never revert to the external tail of his 

 progenitors, except in his embryonic state ? (c) Why 

 do birds never revert to their lizard-like ancestors ? 

 (d) Why does the horse never revert to his five-toed 

 progenitor ? 



The only reply to all these and similar questions is, 

 that there must be a limit to reversion. They probably 

 do revert, when only recently emerged from their 

 ancestral types, by some "break," as horticulturists 

 call it ; but continued selection, natural or artificial, for 

 other more tiseful and important characters, apparently 

 often extinguishes the power of reproducing certain 

 other characters. This law can only be deduced from 

 the fact that animals and plants actually dont go on 

 reverting for ever to all the characters of their ancestors. 

 If they did, there would hardly be any room for selec- 

 tion. It is only by the suppression of some character, 

 or exaggeration of another, or evolution of some new 

 one, that things can become different, and continued 

 selection in any particular direction must, sooner or 

 later, suppress or dwarf some of the least important or 

 disadvantageous parts. 



