tribute greatly to understanding the origins of The plan for this book goes back almost 20 years. Already, at that time, it was possible to recognize organisms. an extraordinary variation in metabolites and To provide the biochemist with a ready over­ processes superimposed upon the basic biochem­ view of the structural diversity of animals, the book includes a simplified version of animal sys­ ical system of animals. Each species, each indi­ tematics; for further information on the classifica­ vidual, in fact each type of cell of the multicellu­ lar organism possesses its own biochemical char­ tion, structure and life of particular animal spe­ acter, and this molecular variety, its biological sig­ cies, the reader should consult the relevant text­ nificance, and its evolutionary development books. It is assumed that the zoologist reader has throw up many interesting questions. The com­ a basic knowledge of biochemistry; important general biochemical facts are in any case given for parative approach that has been so productive at many of the subjects covered. the higher levels of complexity of morphology and physiology can also be used to great effect at I had already completed several chapters of the molecular level. this book by the beginning of the 1970s.