The way in which the lives of all animals and plants are interwoven with that of other animals and plants, often in obscure and unsuspected ways, comes home to man when he contemplates the numbers and variety of living things which exist with him and upon him—that is to say, at his expense and to the detriment of the stores which he accumulates, the clothing with which he covers himself, and the buildings which he constructs. Man not only has carefully taken a number of animals and plants in hand and cultivated them as food-givers, as sources of clothing, and other useful material, but, much to his annoyance, he finds, per contra, that other animals (and plants, too), with similar self-seeking habit, make use of him in his turn, and of his belongings, with a complete disregard of his convenience, treating him and his arrangements as so much available “food-stuff,” and showing no atom of respect to him as the lord of creation. Just as in dealing with the more deadly attacks of disease-producing parasites, so in meeting the destructive invasions made by his fellow-creatures of all sizes and kinds in search of food and shelter—man has to be continually on the alert, and to wage a constant warfare, unless he will consent to see himself and his possessions moth-eaten, fly-blown, worm-burrowed, reduced to fragments and powder. And this warfare he has incessantly carried on with increasing skill and knowledge from the earliest times of which we have any record. The sparrow and the rat, of which there has lately been much talk, are examples of fairly large, easily detected enemies of this kind. The almost ultra-microscopic bacteria—similar to those which produce disease by multiplying in the living body—are examples of the most minute living pests which injure man by causing sourness, putrefaction, and destructive rot in his food and stores. Every year civilised man is gaining greater knowledge of these “ferment organisms,” and vastly increased skill in preserving his possessions, such as food and drink, from the attacks of their ubiquitous swarms. Between the larger depredators, such as birds and rats, and the smallest, such as the microscopic bacteria and moulds (to whom alone putrefaction is due, and without whom it would never occur), there are a host of small troublesome creatures, which belong chiefly to the group of animals called “insects”—beetles, moths, flies, and bugs—which give man incessant occupation in warding off their attacks upon his food, his clothes, his furniture, his buildings, his crops and fruit trees, and his domesticated animals. The study of these things and of the means of grappling with them is the fascinating occupation of those who are called “economic” zoologists and botanists. Of course, in order to carry on their inquiries successfully they have to bring to bear on the questions they investigate as complete and thorough a knowledge as possible of all the kinds of animals and plants, and of their ways of