134 [June, 



It would appear, then, that a large and conspicuous Butterfly, the 

 larva of which feeds on such common plants as hawthorn, sloe, apple, 

 etc., which was counted as a London insect early in this century, and 

 which, less than twenty years ago, was still abundant in certain dis- 

 tricts in England, disappeared, or practically became extinct, in all its 

 widely-separated localities in so limited a period as from ten to fifteen 

 years. 



There are those, I believe, who think the species may be re- 

 habilitated through natural immigration from the Continent. Having 

 the fullest and firmest belief that some of our conspicuous British 

 Butterflies remain British only through occasional immigration in large 

 quantities, I do not share the opinion that Aporia cratcegi is likely to 

 re-establish itself by this means, because, in my opinion, it is a non- 

 migratory species. It is probable that almost any winged insect may 

 be migratory in a sporadic sense, that is, in so far as concerns certain 

 individuals, but supposing such exist in this species, these casual 

 migrants could have little or no effect in re-peopleing the country. 



As to the cause or causes of extinction. I have already alluded 

 to the decadence that appears to be going on in many British Butter- 

 flies. I am of opinion that this is mainly due to occult natural causes, 

 and not brought about directly by man's agency. With regard to the 

 disappearance of this and other Butterflies from the vicinity of this 

 vast and overgrown metropolis, there is perhaps nothing to be wondered 

 at. But in the case of Aporia cratoegi, its disappearance from its 

 country haunts is inexplicable on causes other than natural decadence ; 

 its food-plants are common and universal, and there have been no great 

 changes in the physical condition of its former localities, I do not 

 think the too-rapacious collector is primarily to blame ; but on this 

 point I would express an opinion that when, from other causes, the 

 vitality or stability of a species is in process of being undermined, 

 the few hundreds of individuals taken by collectors in a certain year, 

 in a certain locality, may materially hasten its extinction. 



I will now briefly allude to two other British Butterflies that have 

 become extinct during my lifetime. 



The first of these is GhrysopJianus dispar. In former years this 

 was abundant in many of the large fens of our Eastern Counties, 

 where its larvae fed upon the great water-dock (^Rumex Jiydrolapathum) . 

 It disappeared entirely about the year 1850, and it is probable that in 

 this case physical causes through man's agency were at work that 

 precipitated its destruction. The great fens were drained, and, more- 



