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I had great fear that the excessive cleanliness of the householders of 

 the sea front was positively exterminating the species, an opinion 

 which I think I ventured to express to you at the time. Formerly 

 the " compo " gate-posts were the places where it was most frequently 

 found ; but these said posts having been painted or hearthstoned, or 

 otherwise cleaned, the conclusion that muralis had been cleaned 

 away also was not unnatural. At any rate, I had made several tours 

 of inspection of these said gate-posts, having visited them almost 

 daily for a week or so, without finding a solitary example, when we 

 happened to get a dull, windy day, and several B. muralis were 

 found, together with an unusually large number of B. perla. I did 

 not at the time in any way connect the presence of the insects with 

 the state of the weather, for the positions in which they were found 

 were often by no means sheltered, but subsequent experience 

 suggested to my mind very plainly that it was a case of direct cause 

 and effect. The walls of an old bridge a mile or two out of the 

 town have been a favourite place for muralis as long as I can 

 remember, and on making a pilgrimage thither to see whether they 

 would still prove as fruitful as formerly, one imago only was found ; 

 but a careful scrutiny of the recesses in the walls easily brought to 

 light a considerable number of recently vacated pupa-cases, and 

 fully a couple of score that contained living pupae ; these varied very 

 much in size, — so small indeed were some of them that I thought they 

 must be B. perla, but not one of that species was bred from them, 

 nor have I ever taken it on these particular walls. It was while I 

 was returning from this expedition that the thought occurred to me 

 that it would not be very difficult to see whether there were any 

 Bryophila cocoons on the posts on the sea front of the town where 

 we had found the imagines already referred to. Bryophila cocoons 

 are not easily seen, I admit ; but with a practised eye, plenty of 

 patience, and the aid of a not too sharp penknife, one may in time 

 clear almost any get-at-able wall of most, if not all, the cocoons upon 

 it. I therefore determined to make a thorough inspection of the 

 posts and intervening low r walls along the front. Selecting such 

 times as the roadway was least frequented, I went over them 

 leisurely from end to end, with the result that I found only one 

 cocoon, and that fully half a mile from the spot where I had found 

 the few imagines ; and this cocoon, judging from appearances, was 

 probably an old one, and possibly had been there for several years. 

 I was not surprised at this negative result, for, as I have before 

 mentioned, the posts had been so often cleaned that few of them 

 had any growth of lichen at all upon them. Where, then, did the 

 insects that one occasionally found on them come from ? On pass- 

 ing my experiences of taking them through my mind, it came to my 

 recollection that it was on windy days that they were found, and on 

 windy days only. The obvious suggestion, therefore, was that they 

 had been dislodged from their natural resting-place, wherever that 

 might be, by the wind, and had settled down on the first spot that 



