Taken together, morphology, anatomy and histology are devoted to the study of physical makeup, primarily of adult animals. Morphology deals with the basic composition and form of animals -- how they are built and why they work the way they do. Anatomy digs a little deeper, with much information being gleaned from dissection. Histology delves deeper still, examining animals on a microscopic level.
Physiology concerns itself with living animals and the ways in which their bodies function. Digestion, mobility, respiration and other bodily operations fall into physiology's purview. Embryology follows the course of an animal's life from inception to birth -- or hatching, depending on the animal in question -- through adulthood, procreation and death.
Taxonomy is responsible for the classification and organization of various animals into their respective kingdom, phylum, class, order, family, genus and species. Since before Darwin, taxonomy has been a somewhat malleable branch of zoology, with classifications being altered from time to time as new information becomes available.
Changes within the animal kingdom -- of creatures living or extinct -- are tracked through these four zoological branches. Ecology focuses on the relation of animals to their environment---how some creatures cope with a lack of water, or an abundance of same, for instance, and what changes the environment brings about within a given species. Paleo-fossile and evolution both deal with the alterations within species that have occurred over long periods of time. Heredity looks at the variations between modern animals and their genetic descendants. A horse breeder, for example, might turn to heredity to determine which foal may grow up to be a champion based on parentage.
Zoology and many of its respective branches have been around since humankind first began forming bonds with animals, both wild and domesticated. Egyptian writings track the life cycles of insects and other animal life common at the time. The Hellenistic Greeks and Romans also conducted extensive zoological studies, as did scientists from other ancient cultures. This groundwork gave scientists such as Anton van Leeuwnhoek, Carolus Linnaeus, Charles Darwin and all who came afterward a foundation from which to continue the exploration of the animal kingdom.