Zoology is the branch of biology concerned with the study of animals, including their embryology, structure, habits, distribution, classification and evolution. Some of the current areas of zoological investigation include anatomy, histology, physiology, embryology, teratology and ethology. The field of zoology, particularly the study of morphology and physiology, underwent a significant development due to the Darwinian theory of evolution by natural selection. This facilitated the classification of animals on a genealogical basis and attempts to determine their genetic relationships. Modern classification system for animals is based on the three-domain system of archaea, bacteria and eukaryota. Animals are further classified under the categories of domain, kingdom, phylum, class, order, family, genus and species. This book traces the progress of zoology and highlights some of its key concepts and applications. It is a valuable compilation of topics, ranging from the basic to the most complex advancements in this field. The extensive content of this book provides the readers with a thorough understanding of the subject.