82 [April, 



isolated trees is perhaps the point most dilficult to explain without some 

 such hypothesis. When we find a solitary tree or bush well colonised 

 by the larvae of these species, it is not necessary to assume as it might 

 be in the case of winged species, and as possibly Mr. Porritt does, that 

 their parents all arrived there from elsewhere during the previous 

 winter. The fact probably is that a solitary $ of one species got 

 there say ten years ago, of another spec-ies five years ago, and of a 

 third say two years ago. From the dates of these arrivals the tree 

 continued well colonised by the respective species. 



I think it highly improbable that a (^ hrumata could carry a $ 

 any distance, and if he could do so for some yards, how is he to find 

 the isolated tree? Only by accident. Now the very active ? ? in 

 their no doubt extensive wanderings, when they fail to find a tree or 

 bush at once or near them, are at least as likely to find the isolated tree 

 by accident. I picture these ? ? when they become active in search of 

 a suitable tree or bush, having some instinct by which, either by scent, 

 by the tendency to travel upwards, or in some other way, they are 

 largely successfvil in finding the parent tree or an immediate neighbour; 

 but the proportion that are unsuccessful in this matter must neverthe- 

 less be considerable and in actual numbers really great. These set off 

 in all directions, and anyone who has seen the rate at wdiich one of 

 these moths can cover the ground, must feel fairly certain that no small 

 number go at least as far as the solitary tree, and now and then one 

 must actually come across it. 



When Mr. Porritt says such isolated bushes are even more infested 

 with larvce than others, several explanations occur to one ; but probably 

 the most efiicient, and at least the one that now interests us, is the one 

 I have alluded to : that these larvae are all descendants of an original 

 arrival some years before, and there can be little doubt tliat year after 

 year the instinct of the moths to find the nearest tree brings an undue 

 proportion of them to the only tree available, not a few, however, failing 

 to do so and going off' in all directions, for the most part to perish, but 

 now and then one will reach some isolated tree even more distant from 

 the parent wood, hedge or orchard. 



It is not important to our present discussion, but it may be noted 

 that in various insects l)oth individuals, when flying paired, use their 

 wings. In butterflies the ? often carries the (^. This appears to be 

 usual in Satyrids and Melitteas, whilst in Lycaenids, Pierids, and 

 Argynuids, the (^ is usually the jDorter. 



Betiila, l-tciyutL' : 



March, 1913. 



