138 THE BIEDS OF HELIGOLAND 



15th to the 16th of August, with a very light south wind, a powerful 

 migration of birds occurred. ' From eleven P.M. to three A.M. mil- 



o 



lions of P. gamma were travelling from east to west, like a dense 

 snowstorm.' ' Again, on the nights of 16th, 17th, and 18th, large 

 numbers of P. gamma passed the island, the migrations commencing 

 each evening at eleven o'clock. On the 19th the wind was south- 

 east, the weather fine and calm. In the evening the sky became 

 overcast, and a strong migration of birds took place. From 

 eleven P.M. until two A.M. thousands of P. gamma were again seen.' 

 A thunderstorm, with high winds, subsequently put an end to 

 the migration. These little creatures also follow an east-to-west 

 course of migration, and they adhere to it with as much steadiness 

 and precision as the different migratory hosts of birds which are 

 observed here. That they, too, accomplish their journey in safety 

 is shown by the enormous swarms of them which frequently cover 

 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 migrations 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. 



So far as my observations go, the flights of these insect migrants 

 are composed exclusively of males. In the case of the Hybernia 

 species, in which the females are wingless, this is of course in- 

 evitable. 



Palmen says in his book ' that young birds do not possess an 

 innate knowledge of the necessity of migration, nor are they 

 cognisant of the direction in which the migratory journey must 

 proceed, but have to learn all this from their parents.' Now, after 

 what we have just learned in regard to the above-named moths, we 

 may perhaps be allowed to ask how these insects could acquire all 



