OCCASIONAL ABUNDANCE OF INSECTS. 33 
known entomologist whose long experience and practical 
knowledge we all admit and admire seems to me to have 
rather darkened counsel by an assertion that on the posi- 
tion in which the larve pupate, whether with head up or 
down depends their chance of survival and as I understand 
the theory, when there are many heads up then we have 
a good galw year, but as to why the great majority of 
pupz should be favourably positioned only once in a long 
series of years, we are not told. This idea seems to me 
to bear its own refutation on its face, because from 
everything we know of nature it is certain that were any 
special position of the pupa necessary for normal develop- 
ment, that and no other would be the position adopted. 
Now what conclusion can be derived from all this? So 
far I have attempted to demonstrate that all those theories 
which explain the erratic abundance of galw by foreign 
immigration of any kind, not only are theoretically un- 
sound and unsupported by any evidence in fact, but that 
what evidence we have on the subject at all goes dead 
against any such hypothesis and further if these moths do 
not come from over the sea and as we can hardly consider 
spontaneous generation as an admissible alternative we 
are forced to the conclusion that where Deilephila galii is 
ever found, there it always exists in greater or less abun- 
dance. That I believe to be a true statement, I do not 
think it credible that the pupe he hid for years beneath 
sandhills, I believe that every year galw moths emerge, lay 
their eggs, and ensure an annual succession of the species. 
And moreover I feel persuaded that the road to the ex- 
planation not only of this but of all these phenomenal and 
irrecular appearances among low forms of life les ina 
true apprehension of that state of things which has been 
well named “‘ The Struggle for Hxistence.’ I mean the 
interaction of two very familiar principles: one of which 
