PREFACE 



The idea of writing this book arose from lecturing on hormones 

 to second and third year students of zoology, for whom the subject 

 formed part of a course in comparative physiology. It was found 

 that no introductory book covered the whole subject equally; 

 even Hanstrom's admirable Hormones in Invertebrates (1939) 

 dealt with only a part of the field and was already out of date in 

 1956, when he assured me that he would not be rewriting it and 

 encouraged me to attempt this general survey. 



To do so necessitated evolving a scheme within which to 

 consider and select suitable examples from the mass of available 

 material. This resulted in a comparative arrangement, which 

 should be of general application, since it is based on the actions of 

 hormones, rather than on their sources or on their phyletic 

 distribution. 



The actions of hormones were then seen to fall into three 

 well-defined groups, the kinetic , the metabolic and the morpho- 

 genetic, although these had not all been named nor clearly defined 

 at that time. Subdividing these groups brought together examples 

 acting upon similar effectors, such as muscles, chromatophores or 

 glands, or having similar metabolic actions, such as increasing 

 water excretion, blood-sugar or respiration. Still further sub- 

 division brought together the hormones that stimulate a given 

 action or facilitate a given process and separated them from those 

 having the opposite effects. When consistently adhered to, this 

 approach helped to give a clear picture of hormone actions, to 

 emphasize cases where antagonistic hormones were known and to 

 draw attention to apparent gaps in recorded knowledge. 



In writing the book, invertebrates and vertebrates were placed 

 side by side to show the extent to which both are now known to 

 have hormones with similar actions. Describing the invertebrate 

 examples before those from vertebrates was a deliberate attempt 



