10 



should find two or more groups of insects, different members of 

 which appeared, judging by the genitaha alone, to be more closely 

 related to members of the other groups than to those of their own ; 

 and in the second case we should find insects, obviously from other 

 reasons specifically distinct, ' lumped ' together as a single species, 

 on the ground that they were not yet differentiated in this one par- 

 ticular. We have in fact no reason to suppose either that differen- 

 tiation necessarily takes place simultaneously along various lines, 

 or that it follows a certain routine order in the various lines along 

 which it takes place: on the contrary, all such evidence as we at 

 present possess would seem to point in an opposite direction. A 

 further consideration tending towards the same conclusion is the 

 fact that it is possible in this matter, as in others, that a similarity 

 or even an identity of structure may sometimes be reached along 

 different evolutionary lines. 



" It seems also necessary to remark that this means of distinc- 

 tion, in common with all others, is of far greater value in some 

 groups than in others. In a group, for instance, where there is 

 close resemblance between the members with regard to the append- 

 ages, a slighter difference will be of importance than in a group 

 where tl?e divergences are generally considerable, and in the same 

 way these characters are of much greater value for specific distinc- 

 tion where little or no variation occurs in the undoubted specimens 

 of a single species, than in a case where their characteristics are by 

 no means so constant." 



To return from this digression, which after all only concerns the 

 two species, britoiiiartis and dicti/nnoides, so far as I am at present 

 aware. 



There are two species of this group at any rate that are peculiar 

 to Asia, plotina and prutoiiiedia. The former seems to be the far 

 eastern representative of anrelio, the latter of hritninartis: both show 

 some affinity, as do the corresponding European species, with 

 dictynna, one of the two lowland and sub-alpine species of this 

 group whose range extends from the Atlantic to the Pacific. There 

 is however a marked difference between the two. Dictj/nna, though 

 it varies in detail, is on the whole a remarkably constant species, 

 while atlialia, though preserving a general likeness, is the most un- 

 stable of the whole group. The latter is no doubt the more recent, 

 and whilst the species connected with dutijnna seem to be more 

 ancestral, there are, both in Europe and Asia species connected with 

 atlialia which are almost certainly more recent than itself, and which 

 have distinct affinities with the cinxia-gvowp. These are in Europe 

 deione with its variety — really the older form, as witnessed by its 

 early stages, its neuration, and its geographical distribution — beri- 

 saloixis, and in Asia snltanensis in Sarafshan, airesia in the Altai, 

 Eastern Siberia and Amurland, with its variety chnana in Central 

 Thibet, and belUina in Northern China; possibly also ininerra in the 

 Ala Tau and Fergana, but with this latter species I have no 



