26 



there is abundant evidence, and that the Pierids are among those 

 affected has been amply demonstrated f- as to C. edum it is perhaps 

 not quite so clear, yet we are not without some facts to go upon. 

 It is recorded b}' Darwin that, " One evening, when we were about 

 ten miles from the Bay of San Bias, vast numbers of butterflies, in 

 bands or flocks of countless myriads, extended as far as the eye 

 could range. Even by the aid of a telescope it was impossible to 

 see space free from butterflies .... More species than one 

 were present, but the main part belonged to a kind very similar to, 

 but not identical w^ith, the common English Colias ed naa .'"^^ Then 

 we have Maiden's note written in June of the great edusa year of 

 1877, in which he says, of the individuals seen at Brighton on the 

 6th, "They appeared just landed from France, and were easily 

 caught ; they were flying inland for several days ; the females were 

 by far the most numerous."-'' 



When considering the question of the immigration of butterflies, 

 we are far too apt to jump to the conclusion that they would arrive 

 by the shortest sea route at the Strait of Dover, but to my mind 

 this is quite unnecessary. Far more probable is it that they would 

 follow a course similar to that taken by the great northern streams 

 of migrating birds. For many years the migrations of birds have 

 been very closely studied, and from a vast number of observations 

 made continuously at mnumerable stations, it has been clearly 

 established that they follow^ certam fixed routes, of which two 

 appear likely to apply in a modified form to the present case. The 

 more westerly route, starting from the north-west corner of Africa, 

 passes along the coasts of Portugal, north Spain and western France, 

 to Ushant, where it divides, a portion breaking oft' to our Irish and 

 Cornish and Devon coasts, the remainder following alonfg the north 

 and west coast of France, and giving off streams towards our south 

 and south-east coasts. The more easterly has its origin at various 

 points along the north African coast, and crosses the Mediterranean 

 either to the south-east coast of Spain, along which it passes, or by 

 the islands of Sardinia and Corsica, or by way of the south-west 

 coast of Italy, all three joining up on the south coast of France, 

 thence passing up the Rhone valley, it picks up the valley of the 

 Rhine, and thus reaches the coasts of the Netherlands and northern 

 France, where it joins up with the western route, streams being 

 thrown oft' to our Kentish and eastern coasts.'^' 



Although such evidence as we have in regard to C. eiltisa in this 

 connection may not be very conclusive, there are certain frag- 

 mentary records that, when considered as a whole, are not without 

 significance. First with regard to the great year 1877. For the 



2-^ "Enfc. Mo. Mag.," vol. vii., p. 18; vol. ix., p. 246. "Proc," 1899, 

 p. 47. 



•^■^ Darwin. " The Voyage of H.M.S. Beagle," p. 158. 



2^ H. C. Maiden, in " The Field." ' Ent. Mo. Mag.," vol. xiv., p. 40. 



2-^ Eagle Clarke. " Studies in Bird Migration," vol. i., p. 72. 



