such as rearing from one batch of ova, leave no room for doubt as 

 to their identity) occasionally exhibiting one or more of the very 

 characters which we are accustomed to regard as distinctive of 

 another species, the whole genus being still in a condition of flux 

 sufficient to lead to frequent instances of atavism." 



It will be observed that these remarks are applied only to the 

 athalia-gvoup, and so far as the European species are concerned 

 this is the only group at all noticeably affected ; for though occa- 

 sional doubts might arise in another group between certain speci- 

 mens of (Udi/iiia and tiin'a, the specimens in question would rarely, 

 if ever, be European ones. But when we come to look at the genus 

 as a whole, the same difficulties would be experienced, probably in 

 almost as acute a degree, in the aminia-gvonp in North America 

 and the f/», cm group in Central and Eastern Asia. 



I am using the terms athalia-gron-p, ai(rinia-group and ciii.ria- 

 group for the three divisions into which the palfearctic species of the 

 genus naturally fall, not because these are all really the most typi- 

 cal species of their respective groups, but because our only three 

 British representatives of the genus each belong quite distinctively 

 to one of the three, and I hope by thus connecting each group with 

 its British representative to make this paper both more interesting 

 and more intelligible to those whose studies are more particularly 

 concerned with our British fauna. There remains, however, another 

 group, confined to the nearctic region, which may be called the 

 ?{'/■////( f /-group, which takes the place, on a somewhat different evolu- 

 tionary line, of the athalia-grouTp in America, where the latter, 

 strictly speaking, is unknown. 



I suppose that the writer of a paper on any genus of insects would 

 be expected to atteiaipt something in the nature of a history of the 

 genus, though on such an occasion as the present anything more 

 than a mere sketch would be out of place, and it must be at once 

 admitted that anything more would also be impracticable, for the 

 genus occupies so vast a territory, such immense portions of which 

 are entirely, or almost, unexplored, that our knowledge even of the 

 imagines is extremely fragmentary, whilst our ignorance of the early 

 stages of the various species, outside those which inhabit the well- 

 worked portions of Europe and some few oases of knowledge in 

 America, is profound. 



How minute indeed are the scraps of our puzzle, and how many 

 of them are still to seek, may be gathered from the misconceptions 

 which surround some of even our well-known European species. I 

 do not wish just now to touch on such questions as the specific 

 value of such forms as brito)iia)tis and dictynnoides, but there are 

 two points to which I must refer, since they have an important 

 bearing on distribution, and indeed on the whole past history of the 

 genus. These two points are the specific distinctness of vierope from 

 aurinia, and of raria from part/ieuie. The two former species are, 

 I believe, separated, in time, by almost the whole palfearctic species 



