Ixvii 



of their being other than perfectly good and true species, in other alpine 

 localities intermediate forms do occur, proving that the two or more 

 species there blend together. He found cases also in which the for- 

 mation of two or more distinct species was not quite complete, as 

 proved by the occurrence of a very few individuals of the connecting 

 varieties. Indeed authors had accepted these species as perfectly 

 good ones, until further research revealed the existence of these rare 

 varieties, when they were just as ready to treat the whole as varieties, 

 as they were formerly to consider them as species. The fact of a 

 species existing, structurally and functionally, as a species in oue 

 locality and as a mere variety in another, was not to be explained away 

 by the argument, that the species were originally distinct, but had 

 become blended by hybridization ; for the effect of such hybridization 

 after a few generations would have been to blend the whole of the allied 

 species into one variable form ; besides it would only shift the problem 

 a step further, and we should have to inquire how the species origi- 

 nated in the first instance. There was no alternative for a naturalist 

 demanding a rational explanation of such facts, but to accept the con- 

 clusion that species have no absolute permanent existence, but that 

 changes intermittingly and slovvly take place by their spreading 

 over wider and wider areas, and adjusting themselves in structure 

 and habits to the altered nature of the local conditions. Where there 

 are numerous varieties in a locality, the process of variation and adapta- 

 tion has not been completed ; where well-defined species occur in more 

 distant situations, the adjustment is, for the time, accomplished, and 

 the connecting varieties between such species and their sister-forms, 

 existing elsewhere, only betray the gradations of modification which 

 have been passed through. I may be permitted here to remark that I 

 have myself recorded a series of facts similar to those published by 

 Herr von Kiesenwetter, with regard to the Heliconiidae of South 

 America, and have given a precisely similar explanation of them, so 

 long ago as 1862, in the twenty-third volume of the Transactions of 

 the Linnean Society, page 530. 



The memoir of Herr von Kiesenwetter, as well as the series of 

 facts brought out by myself on the Heliconiidae, prove, I think, the 

 importance of the study of Geographical Distribution, in con- 

 nection with the supreme question of the Origin of Species. 

 The facts of distribution, correctly and minutely noted, will pro- 

 bably supply more satisfactory data for the discussion of this question 

 than any other class of facts in the domain of Natural History. 



