OCCASIONAL ABUNDANCE OF INSECTS. 35 
establish anything like a reliable record. For example in 
that restricted area which we call the Wallasey sandhills, 
a locality perhaps better watched than any other similar 
spot; I believe that one hundred moths might exist for a 
lifetime of normal duration and never be seen at all. But 
say unmerciful disaster following year after year has brought 
down their numbers to no more than ten~ females. A 
number I indeed hold as absurd, being too near the point 
of actual extinction which I maintain has never so far 
been reached. Now credit each female with fifty fertile ova 
a very moderate allowance and assuming in the progeny an 
equal proportion of the sexes it is not a difficult calcula- . 
tion to prove that allowing all the ova to reach maturity, 
only three years would produce the enormous total of 
300,000 perfect insects. 
But of course the total number of ova laid never do 
reach maturity, they are ruthlessly mown down in every 
stage of their career, death dogs their every footstep, birds, 
mammals, hosts of other insects, spiders, ichneumons 
beetles, floods, moving sands, disease of all kinds, and last, 
but not least, entomologists, or rather collectors, when 
they have the chance, thin their attenuated ranks from 
the ovum to the perfect insect. And the comparatively few 
imagines which result represent the balance, the small 
fraction, between the many that have perished and the 
slightly more who were born. 
Thus then the question seems so far cleared that it is 
obvious that any diminution or mitigation of the des- 
tructive agencies, would in one or a short series of years 
quite sufficiently account for those seasons of singular 
abundance without suggesting anything abnormal in the 
ontogeny of the insect itself. 
The next step then in the enquiry is to consider the 
nature and incidence of these destructive agencies what- 
