ON PROGRESS IN THE STUDY OF 

 VARIATION. 1 



( Continued. ) 



WE have now to examine the special case of local 

 varieties or races, and to consider how the phen- 

 omena they present may best be turned to account in the 

 attempt to investigate objectively the origin of species. It 

 is here that we are especially dependent on the efforts of the 

 collectors. Without great collections little progress can be 

 made, but by modification of the usual practice their utility 

 for the solution of these problems might be much increased. 



It is a fact familiar to every naturalist that in very many 

 species individuals living in different areas are dissimilar, and 

 that by these dissimilarities the species may be broken up 

 into local races. This phenomenon of local differentiation is 

 so common that species in which it is not in some degree ap- 

 parent may almost be regarded as exceptional. The differ- 

 ences may be exceedingly slight, and appreciable only to a 

 person who has had long experience of the form in question ; 

 or, on the other hand, they may be so decided that it is only 

 after special study and examination of series of specimens 

 from many localities that the local races can be recognised 

 as belonging to the same species. 



In addition, too, to cases of this latter order, in which 

 reason has been found for uniting dissimilar local races, 

 there are numberless instances in nearly all orders of animals 

 and plants where it is practically certain that forms which, 

 on account of their dissimilarity and distribution have been 

 considered as distinct, might with almost equal propriety be 

 regarded as local races of the same species. Local differen- 

 tiations of this kind are the despair of the systematise How 

 may species be distinguished from local forms ? How great 

 must the differences be, and in what organs must they ap- 



1 Corrigenda to part i. of this article, which appeared in the last 

 volume of Science Progress. 



P. 556, line 3 ; for " most subalpine " read " most southern ". 

 P. 556, line 7 from bottom ; delete "wings". 

 P. 565, line 4 ; for " monacha " read " eremita ". 



