136 fJune, 



the mainland seem to prove, iji many cases, barriers to that introduc- 

 tion of fresh blood necessary for the recuperation and continuance of 

 the race. 



With us, the continued extension of our large towns, and the 

 inevitable smoke and other insanitary conditions, have no doubt 

 caused many species to become more and more localized, and so also 

 has the high state of cultivation contingent upon the necessities of a 

 rapidly increasing population over a restricted area ; and localization 

 may generally be looked upon as the first step to extinction. 



British Butterflies may be divided into several more or less 

 delimitated groups as regards their ability, or othervrise, to resist 

 decadence. 



In the first there are those, and happily they are the largest 

 division (although they include some distinctly injurious species), 

 which are of comparatively general distribution, and if some are dis- 

 tinctly localized, it is usually through natural physical conditions, such 

 as latitude, altitude, &c., and they show few, if any, signs of decadence. 

 Moreover, in this group, and even in our familiar " Cabbage Whites," 

 there is undoubted occasional immigration in large numbers in some 

 of the species ; in others not at all. 



There is another group, the members of which are sometimes 

 extraordinarily abundant, that would probably soon become extinct 

 but for the invasion at uncertain intervals by migratory swarms ; and 

 indeed there seems reason to believe that they do become temporarily 

 extinct, but experience proves that the chances of their utter extinction 

 are remote. Here may be placed Golias JEdusa and Si/ale, and perhaps 

 Vanessa cardui. 



Then comes a small contingent, consisting of species which there 

 is no evidence to prove ever breed here, or at any rate, have done so 

 in recent times, but yet occur in an irregular manner to an extent 

 that leaves little fear for their extinction. Such are Pieris Daplidice, 

 Argynnis Lathonia, &c. ; and here also may be placed Vanessa Antiopa : 

 all of these may be said to be more or less sporadic, but the last 

 named, when it does occur, is usually in considerable numbers and 

 widely spread. 



Again, there are those which, while inhabiting the most restricted 

 localities, continue on from year to year in undiminished numbers, 

 notwithstanding the onslaughts made upon them by collectors. Ses- 



