The science that deals with knowledge of animal life. Together with botany, the science of plants, it forms biology, the science of living things. With the great growth of information about animals, zoology has been much subdivided. Some major fields are anatomy, which deals with gross and microscopic structure; physiology, with living processes in animals; embryology, with development of new individuals; genetics, with heredity and variation; parasitology, with animals living in or on others; natural history, with life and behavior in nature; ecology, with the relation of animals to their environments; evolution, with the origin and differentiation of animal life; and taxonomy, with the classification of animals.