ABSTRACT
The word reproduction conveys the idea of production of additional individuals of that species, either singly or in large numbers, depending on the experience of the reader among the various groups of animals. This chapter provides an overview of all reproduction in all animal groups. Some of these difficulties are summarized. First, the fact that most zoologists are more familiar with vertebrates than with invertebrates makes it likely that conditions in the vertebrates will seem to be the norm or even considered to be universal. Second, in vertebrates most of the obvious reproduction occurs in the adult state, which is defined on that basis. Third, most zoologists learn early the developmental sequence of higher vertebrates, involving a fertilized egg, multiplication and diversification of cells, and development through embryonic or larval forms into adulthood. Fourth, in many species the manner of production of one individual may be quite different from that of other individuals.
