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literally in myriads, and all taking the same upward course 

 until they were lost to view. At the time I placed but little 

 importance on the curious sight that I had seen, but have 

 many times thought of it since ; and I am fully inclined to 

 agree with Mr. South in what I take to be his view, that we 

 had witnessed the initial movement of an extensive migration. 

 I have thus far dealt chiefly with the collecting together of 

 the scattered fragments of evidence that bear upon the subject 

 under our notice ; and it remains for me, in concluding, to 

 consider this evidence as a whole, and as such, to draw 

 conclusions from it. In the first place, then, we have 

 abundant evidence that migration does take place. In the 

 case of Pieris brassicce we have been able to trace the migra- 

 tory swarms crossing the sea, landing on our coasts, and 

 ultimately distributing themselves over the country. The 

 sudden abundance of Vanessa cardui just at the time when 

 such vast multitudes were observed immediately to the south 

 of us, and moving in our direction, is also a significant fact, 

 and the swarms of Plusia gamma and other species passing 

 the Heligoland light " all going west," when taken in 

 conjunction with the minor facts already detailed, point 

 strongly to the conclusion that some cases of unusual 

 abundance are due directly and solely to immigration. But 

 it is equally certain that this theory will not hold good in 

 all cases ; the swarms of larvae that from time to time 

 devastate portions of our forests, must have been reared on 

 the spot where we find them, as must also the quantities of 

 Deilephila gain larva that have from time to time thrust them- 

 selves upon our notice, notably in 1888. This last outburst of 

 this species, however, may perhaps give us a very good clue to 

 the solution of the problem. It will be remembered that 

 before any of the larvae were seen, imagines corresponding in 

 all respects with those known to inhabit the warmer countries 

 of Continental Europe, were taken in various parts of this 

 country, including Kent, Lancashire, Ireland, etc. ; the 

 numbers, however, were comparatively small, but they were 

 succeeded by an " unusual abundance " of larvae ; that these 

 larvae resulted from the imagines of whose presence we 

 became aware by some of them being taken, there can be no 

 doubt ; and there is some very strong circumstantial evidence 

 that the imagines were migrants. It is, however, by no 

 means certain that an arrival of moths would be always 

 followed by an abundance of larvae ; but in this case, it will 

 be remembered, they arrived at a time when, by reason of a 

 hot summer, the conditions were favourable for their de- 



