It is because biologists see these parasites so plainly all down through the scale of living things that they are so sceptical of accepting any other cause of human disease until all possibility has been excluded of its being caused by some parasite or other, too small to be seen even by using the best microscopes.
My sympathy for this long-horned beetle would be keener did I not read that its larval self is spent inside the wood of the pines and firs of our forests, doing great damage to them.
When one is puzzled to know why any living thing should be burdened by such antler-like antennæ, let him remember the peacock’s tail and the bird of paradise’s plumage and be content to know that the laws of evolution are not yet fully known, and that, given time and growth, almost any form can be evolved.
TWO-WINGED INSECTS
(Diptera)
Years ago in Berlin, my German landlady called me in as an expert to decide a controversy between her children and herself as to whether a frog had four legs or six. It seemed strange to me then that a grown-up woman should not know the number of a frog’s legs. Yet there will be many who read these pages who do not know how many wings a fly has. And flies are much more important than frogs.
In fact the mosquito and the house fly, both included in the order of the flies, probably cause more deaths and are more dangerous to human life than any other creatures in the world.
These portraits are of a few only of the vast myriads of forms of two-winged insects which haunt the world. Were I to photograph just one individual of each different species which inhabit the globe, I would have to spend a lifetime doing it, and when it was finished it would make five hundred volumes about the size of this one.