34 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
is that among all low forms of life the capability of increase, 
the potentiality of enormous and rapid multiplication is 
exceedingly high, so much so that the mere geometrical 
increase of even a single pair would theoretically m one, 
two or three seasons result in far more than the numbers 
actually produced even on the most favourable occasions 
of abundance. The other principle being that the waste 
of immature life is also so immense, the forces of destruc- 
tion arrayed on every side so active, so unceasing, so 
innumerable, that of any given species in every year, the 
actual survivals bear to the possible survivals only the 
very smallest proportion. ‘That is to say, the number of 
mature individuals of any species of insect we see around 
us, represents only the small balance between a vast 
generative and a vast destructive power, and in its varia- 
tion is an index not of a variable productive capability on 
the part of the race, but of a variable application of the 
agencies of destruction. 
Those who have studied any of the lower forms of life, . 
know well what a worse than Mirza’s bridge is the course 
of any such existence, how of the millions of ova laid 
only the few units struggle into the perfect light of 
maturity; indeed so imminent so inexorable are the 
dangers that ever beset all such life that among insects at 
any rate, the greater part of that variety of structure and 
appearance which we see so manifest, seems to have been 
brought about in a great measure by the shifts necessarily 
resorted to, and the disguises adopted, in order to evade 
utter destruction. And now to consider the case in the 
light of this axiom which I consider as the key of the 
problem. I hold then that Dewlephila galw never QUITE 
dies out, I maintain that in the desolate places where this 
species breeds, the unfrequented coasts, the lonely marshes, 
the solitary wastes there are far too few observers to 
