ECONOMIC IMPORTANCE OF ZOOLOGY Finally, it is necessary to say a few words about the economic importance of zoology. The breeding of domestic animals is a great industry, after the rearing of food plants, the largest and most widespread that there is. It has been extraordinarily suc cessful in producing breeds of sheep, cattle and horses, fitted for all conditions and uses. But its methods have been purely em pirical, and consequently thus necessarily slow and wasteful in application.
It is certain that the application of modern genetics to animal breeding will lead to advances as great as those which have already been effected in the establishment of new races of cultivated plants. (See ANIMAL BREEDING, BREEDS AND BREEDING.) The damage that animal pests, especially insects, do to crops, amounts perhaps to more than a hundred million pounds a year. These ravages can only be controlled by methods laid down by zoologists. The establishment of these methods depends on a full investigation of the life history and habits of the pest, and of all the factors in its surroundings which influence it. Climatic con ditions, distance from water, alternative sources of food, the efficiency and mode of application of poisons, parasites and dis eases of the pest, and animals that prey on it, have all to be inves tigated by the ordinary methods of bionomical research. (See ENTOMOLOGY : Economic Entomology.) Fisheries (q.v.) present many problems, variations of the catch from season to season, the extent to which the breeding stock is becoming depleted, new fishing grounds, the possibility of artificial culture are all problems of the greatest complexity which fall within the province of the zoologist.
The control of insect-borne diseases of man must rest on meas ures determined by zoologists, and their work may touch human affairs even more directly. (See PARASITOLOGY.) The results of a differential fertility of different sections of a nation's population, and of a mixing of races are things of the greatest importance to Governments, and should receive their attention to a much greater extent than they in fact do. But they can only be investigated by men who include zoology in their equipment, whether they be biometricians or followers of some other school. (See BIOMETRY; EUGENICS ; POPULATION.) The purpose of this article is to indicate, very imperfectly, the interrelationships of the various types of study which are included under the wide heading of zoology. Each is more fully explained in a separate article, to which reference should be made.
The more important of these are :--The articles dealing with the separate phyla and other groups; PROTOZOA ; SPONGES ; COELEN TERATA ; PLATYHELMINTHES ; NEMERTINEA ; NEMATODA ; AN NELIDA ; ARTHROPODA ; MOLLUSCA ; POLYZOA ; BRACHIOPODA ; VERTEBRATA ; CYTOLOGY ; HISTOLOGY ; EMBRYOLOGY ; HEREDITY ; EVOLUTION ; PALAEONTOLOGY ; ZOOLOGICAL REGIONS ; ECOLOGY ; MORPHOLOGY ; BIOMETRY ; PHYSIOLOGY ; ANIMAL BEHAVIOUR.