As the title indicates, the theme of this book is the functions of biochromes in animals. Recent works on zoochromes, such as those of D. L. Fox (1953), H. M. Fox and VEVERS (1960) and VUILLAUME (1969), have been concerned primarily with the chemical nature and the taxonomic distribution of these materials, and although function has been considered where relevant this has not been the centre of interest and certainly not the basis for the arrangement of the subject matter. Functional significance is a profitable focus of interest, since it is the one theme which can make biochromatology a discrete and integral subject, and because it is the main interest in all biological fields. At present chromatology seems to be a particularly schizoid subject since it is clear that in metabolic functions biochromes are acting in a chemical capacity whereas integumental pigments function mainly biophysically, in neurological and behavioural contexts. It is profitable to attempt an integration by studying the functions of as many chromes as possible, from all aspects.