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conditions necessitating its commencement extended their area. 

 How those individuals first commenced to fly over the sea it is 

 impossible to say. Before the migratory habit w^as initiated they 

 can have had no knowledge of Brazil. Perhaps the general 

 direction of the winds which are westerly at the present day and 

 may have been so at that period, had their influence on these 

 early flights. In the meantime, inheritance will have had ample 

 time to accomplish its work, and the accumulated experiences of 

 thousands of generations will have sufficiently developed the sense 

 of locality by means of which these flights are able to find their 

 way over the pathless tracts of the Atlantic at the present time. 



Herr Gatke in several places in his work compares the so- 

 called migrations but properly speaking emigrations, of insects 

 with those of birds, bringing forward the case of the former as an 

 objection to the theory that the sense by means of which birds 

 find their way has been acquired and transmitted through 

 inherited experience. 



To the writer the migrations of insects are of quite a difi^erent 

 nature to those of birds. In the first place they are of most 

 irregular occurrence, and are declared by the author himself to be 

 due to the prevalence of certain meteorological conditions. The 

 only bird migrations which they at all resemble are those of 

 Pallas' Sand Grouse, which latter are emigrations in the true 

 sense of the word. It is generally assumed that this species has 

 always followed the same course during its irregular move- 

 ments, but to the writer it seems very probable that other flights 

 may have emigrated to quarters in opposite directions. In the 

 second place the insects composing these flights never return to 

 the place of their departure and it is not known for certain that 

 they ever land on a coast at any distance away. 



In the third place it is very doubtful if an insect like Plusia 

 gamma, to which Herr Gatke specially refers, has the power of 

 crossing the North Sea ; its speed of flight being no greater than 

 that accomplished by an entomologist intent on its capture, as the 

 writer knows from experience. The simultaneous appearance in 

 Lincolnshire of this species in great abundance, with the advent 

 of large flights at Heligoland, has no significance whatever. This 

 abundance is by no means confined to the former county and has 



