128 



THE YOUNG NATUEALIST. 



(I.) Of the butterflies upon our existing lists " one at least is already 

 extinct, several are only keeping on our lists by immigration, and a still 

 larger number, while common where they occur, are disappearing from 

 extensive districts, and not again spreading over them.'" 



(II.) " The earlier writers on entomology mention a considerable number 

 of species as natives of Britain, that are not now to be found." 



(III.) Nothing like the same proportion of species in other groups are 

 becoming rare or extinct. " A few species may have done so, but none that 

 were even generally abundant, and in every (other ?) group the new additions 

 to our fauna have far exceeded those that have disappeared or become rare." 



(IV.) Comparing the whole number of species of the larger Lepidoptera 

 found in the Palsearctic region with the number of British species, we find 

 " that in proportion to the other groups (except Burnets) either singly or 

 or together, we have less than half the number of butterflies that we ought 

 to have." 



The fourth of these statements may, I think, be very shortly dismissed 

 from our consideration, for though I believe it to be perfectly true, I do not 

 think any deduction, such as Mr. Robson would draw, can be legitmately 

 drawn from it. Of course if it were certain, or even probable, that we 

 originally started with a number of species of butterflies only less than the 

 total number of Palesearctic species, in proportion as the number of our 

 species of larger Heterocera are less than the total number of Palesearctic 

 species, Mr. Bobson's table would be cogent evidence that our butterflies had 

 already very considerably diminished in number. But surely it is far more 

 likely that there was once a time when the species of butterflies over the 

 whole of the Palsearctie region was very small, that from these few species 

 the others were developed, and that this developement of species was more 

 rapid and extended where the conditions were more suited to sun lovers. 

 That the table, in fact, is no proof of decrease of species in our Islands, but 

 only of less increase. 



With regard to the third premise, I would remark that it is hardly fair to 

 lay any stress on the fact that in every group of Lepidoptera, except the 

 butterflies, " the new additions to our fauna have far exceeded those that 

 have disappeared or become rare," for this is, of course, explained by the fact 

 that the butterflies are so much more conspicuous than the other groups. As 

 to the rest of the premise, it is a question of fact as to which Mr. Eobson is 

 far better able to judge than I am. 



With regard to the second premise I think Mr. Robson takes rather an 

 extreme view, and I do not consider that it has all the significance which he 

 appears to attach to it. Some of the old records may be trustworthy, but 



