24 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
a problem in Entomology. And now I will examine this 
theory a little more closely. It is that vast numbers of 
the imagines—the moths—of Deilephila galwi cross the 
sea from somewhere and replenish these islands during 
the ‘ Galii”’ years. Now it is at once obvious that for a 
scientific explanation this theory is not nearly definite 
enough. We want to know not only whence but also 
why they come. And be it noted, the only evidence that 
they come at all, is in the fact that they appear in 
England suddenly, without visible progenitors. 
But when we come to ask our theorists, whence are 
these swarms derived? they decline to commit themselves 
to any definite reply. It might either be from the land 
of the midnight sun or from beyond Atlas for all we are 
told to the contrary. Mr. Tugwell and Mr. Dale indeed 
conjecture from Holland and Belgium, but we have no 
evidence, not a shred, that on those particular years, this 
moth was in unusual abundance in the Low Countries. 
It is a pure assumption that the migration, 1f migration 
there were, originated on those coasts, based on no better 
reason than that these form the nearest land to the littoral _ 
of Kent and Essex where the larvee were abundant: but 
they were also no less abundant in the Wallasey sandhills 
and were not discovered at all on the coasts of Hampshire 
and Dorset, which are certainly much nearer the Belgian 
shore than is Crosby or Wallasey. 
And if it is thus difficult to answer the question of 
origin, it is impossible to answer the question of cause. 
We are at once involved in the whole theory of migration. 
Now it here occurred to me that this term migration was 
used in much too vague a way. ‘There are two distinct 
and indeed incompatible ideas here covered by the same 
term. One of these, not both or either, must be the 
migration, which compels galw from the Continent, and 
