This work is a departure from the classical presentation to the student of animal parasitology. It is a reflection of the new era in parasitology, wherein the knowledge and tools of other sciences, such as biochemistry, microbiology, immunology, physiology, and so on, are brought to bear upon a field expanding beyond systematics and morphology. The author places major emphasis upon the living parasite and the host-parasite relationship. In particular, an attempt is made to analyze the factors which control the growth, maturation, and reproduction of parasites in relation to the physiology of their hosts and the properties of the environment. No attempt has been made to cover the entire field of human or animal parasitology. Many of the better known human parasites are considered as are the animal parasites which are easy to obtain from the animal kingdom for the purpose of presenting the dynamics of the groups involved. Morphology