Now if its shape is unaltered its surface will be increased only a hundredfold, and ten times as much oxygen must enter per minute through each square millimetre of skin, ten times as much food through each square millimetre of intestine.
When a limit is reached to their absorptive powers their surface has to be increased by some special device.
Unfortunately the cross sections of their bones were only a hundred times those of Christian, so that every square inch of giant bone had to support ten times the weight borne by a square inch of human bone.
As the human thigh-bone breaks under about ten times the human weight, Pope and Pagan would have broken their thighs every time they took a step.
It can go in for elegant and fantastic forms of support like that of the daddy-longlegs.
But there is a force which is as formidable to an insect as gravitation to a mammal. A man coming out of a bath carries with him a film of water of about one-fiftieth of an inch in thickness. A wet mouse has to carry about its own weight of water.
So the resistance to falling in the case of the small animal is relatively ten times greater than the driving force.
An insect, therefore, is not afraid of gravity; it can fall without danger, and can cling to the ceiling with remarkably little trouble.
A typical small animal, say a microscopic worm or rotifer, has a smooth skin through which all the oxygen it requires can soak in, a straight gut with sufficient surface to absorb its food, and a single kidney.
Increase its dimensions tenfold in every direction, and its weight is increased a thousand times, so that if it is to use its muscles as efficiently as its miniature counterpart, it will need a thousand times as much food and oxygen per day and will excrete a thousand times as much of waste products.