THE MIGRATION OF BUTTERFLIES. 343 



the east coast of England, and which can only be explained as the 

 result of an immigration. Besides P, gamma large numbers of 

 Gastropacha neustria, Agrotis graminis, and other species, are 

 represented in such migratory swarms. It has been suggested 

 that these insects are attracted by the light of the lighthouse, 

 and that, consequently, it is only around the latter that they are 

 seen in such quantities; this, however, is contradicted by the 

 migrations of Hybernia defoliaria and H. aurantiaria, these 

 insects sometimes making their appearance during strong migra- 

 tions of Larks in October, when large numbers of them may be 

 found in the course of the night, as well as on the following 

 morning, from one end of the island to the other. Now it is 

 quite impossible that these moths should be able to collect 

 experiences of any kind during this single migration of their 

 life, which, moreover, is performed in the darkness of night 

 across a wide expanse of water; and even if they did these 

 would be perfectly useless, for these migrants die shortly after 

 their autumn migration without having produced further offspring 

 to which they could commit their experiences, either by hereditary 

 transmission or by personal instruction." 



On the subject of migrating Dragonflies, Herr Gatke 

 remarks : — 



"Another very peculiar phenomenon, also intimately connected 

 with thunder-storms, is the regular but temporary appearance, in 

 millions, of the large Dragon-fly (Libellula quadripunctata) before 

 such disturbances. Countless swarms of these insects make their 

 appearance all of a sudden during the calm sultry hours preceding 

 the catastrophe, while thunder-clouds gather on the horizon, and, 

 heaped upon each other, project into the blue ether beyond, like 

 so many giant mountains of snow. 



" The direction whence these insects proceed cannot be 

 ascertained, nor do they arrive in swarms or companies, but 

 solitary individuals or scattered groups probably congregate on 

 the spot in one vast throng. The assembling individuals or 

 groups must, however, follow each other in very rapid succession, 

 for in a short time the face of the cliff, still illumined by the 

 sun, all the buildings, hedges, and dry twigs on the island, are 

 covered with them. Nor is it necessary for the occurrence of 

 this phenomenon that the storm should actually discharge itself 

 over Heligoland, or even in its immediate neighbourhood, but 



