§1.5 TYPES OF HORMONES 7 



and its growth and reproduction. These processes must be con- 

 trolled to fit the frequent changes both within the animal and in 

 its environment. At different times of the day, or the tide, or the 

 year, the energy must be directed to different purposes, to serve 

 the needs of both individual and race survival. The greater part 

 of this control is achieved by the nervous system ; but hormones 

 may com.e in at almost any point, sometimes independently, but 

 more often in direct or indirect response to nerve stimulation. 



It is not merely convenient to review the hormones in relation 

 to their actions; it also allows of some interesting comparisons 

 being made between those having similar actions in invertebrates 

 and vertebrates, and reveals a notable degree of correlation 

 between some of their actions and the sources from which the 

 hormones come. It also shows certain striking gaps : some animals 

 lack hormones with particular actions; many invertebrate phyla, 

 or classes, lack hormones altogether. It may be supposed that in 

 many cases the main detectable actions of a hormone represent its 

 physiological functions within the normal animal; but other 

 actions, which are apparent experimentally, may be accidental 

 and without true functional significance. Their actions will be 

 considered under three main headings : 



(1) Kinetic, or the control of effectors (§ 1.51 and §§ 3 and 4); 



(2) Metabolic, or the control of cell biochemistry (§§ 1.52 and 5) ; 



(3) Morphogenetic, or the control of growth and differentiation 

 (§ 1.53, and Part II, to be published separately). 



Each of these groups can be further subdivided in relation to 

 the particular organs or processes controlled (Table 1). This 

 grouping of hormones is not yet widely used; but it has been 

 found in practice to afford a very good working framework within 

 which to consider the available information, with the minimum of 

 ambiguity or overlap. It has been accepted in a recent presenta- 

 tion of crustacean hormones (Carlisle and Knowles, 1959), together 

 with the terms kinetic and endocrinokinetic suggested to them by 

 the writer (Carlisle and Jenkin, 1959). The term kinetic hormone 

 corresponds to their previous term of ''energetic hormone" 

 (Knowles and Carlisle, 1956). 



