The truth of this has been demonstrated again and again. A pair of rabbits, for example, would in the most favourable circumstances increase in four or five years to a million. The roe of a cod may contain eight or nine millions of eggs. More appalling still, the female of the common flesh fly will at one time deposit 20,000 eggs. At this rate of increase it has been calculated that, in less than a year, a single pair would produce enough flies, if these were not devoured by their natural foes, to cover the whole surface of the globe to the depth of a mile and a quarter! But all this does not, of course, make it clear why in a beneficently ordered world such a necessity of slaughter should ever have been allowed to arise. Darwin, as we have said, tried hard to take the most favourable view of the whole process. He thus concluded his chapter on the struggle for existence; "When we reflect on the struggle, we may console ourselves with the full belief that {56} the war of nature is not incessant, that no fear is felt, that death is generally prompt, and that the vigorous, the healthy, and the happy survive and multiply." And these are the words with which he concluded the _Origin of Species_: "Thus from the war of nature, from famine and death, the most exalted object we are capable of conceiving, namely the production of the higher animals, directly follows." But a year or two later he shewed that his mind was by no means at rest on the matter, by writing in this strain to his friend Asa Gray: "I own that I cannot see as plainly as others do, and as I should wish to do, evidence of design and beneficence on all sides of us. There seems to me too much misery in the world. I cannot persuade myself that a beneficent and omnipotent God would have designedly created the Ichneumonidae with the express intention of their feeding within the living bodies of caterpillars, or that a cat should play with mice.... I am inclined to look at everything as resulting from designed laws, with the details, whether good or bad, left to the working out of what we may call chance. Not that this notion _at all_ satisfies me.... Let each man hope and believe what he can. Certainly I agree with you that my views are not at all necessarily atheistical."[2] {57}