10 INTRODUCTION 



Among vertebrates all the endocrinokinetic hormones are 

 secreted by the adenohypophysis (anterior lobe of the pituitary 

 body) ; but so also are hormones with such morphogenetic actions 

 as stimulating the growth and maturation of the gonads. Yet the 

 term trophic or tropic has been applied indiscriminately to both, 

 as in the case of the gonadotrophins, of which the interstitial- 

 cell-stimulating hormone, ICSH, is endocrinokinetic and causes 

 hormone secretion from the gonads, but the folUcle-stimulating 

 hormone, FSH, is morphogenetic and causes their growth. There 

 are as yet no separate names for the similarly separable actions of 

 the thyrotrophic hormone, TSH, or of the adrenocorticotrophic 

 hormone, ACTH ; but there is a mounting body of evidence to 

 show that the two types of action are often, and perhaps always, 

 due to distinct, albeit closely similar hormones (§ 4.2). If in some 

 cases the two actions are really inseparable, they may perhaps be 

 likened to the motor and trophic actions of one and the same 

 nerve. 



There are still a few effectors for which no example of kinetic 

 hormone control is known: namely, luminous and electric organs 

 among those usually controlled by nerves, and flagella and nema- 

 tocysts among those for which no internal control is known. 



1.52 METABOLIC HORMONES 



The metabolic hormones are concerned particularly with the 

 control of metabolic activities, at the physico-chemical or bio- 

 chemical level, within the cells of the animal, e.g. with adjustment 

 of respiratory rate (§ 5.1), supply of sugars and proteins to the 

 tissues (§ 5.2), and their electrolyte and water balance (§§ 5.3 and 

 5.4). Such processes often have a basic rate that seems to be an 

 intrinsic or genetic property of the cells which carry them out. 

 The rates are rarely under nerve control, but hormones may 

 induce changes in them; in many instances, a pair of hormones 

 act together, one increasing the rate and the other decreasing or 

 inhibiting it. This is particularly clear in the control of electrolytes 

 and water in the vertebrate kidney (§ 5.3). Many of the metabolic 

 hormones in Arthropoda are products of neurosecretion, and 

 stimulate the rate of the process in question but are themselves 

 subject to nervous inhibition. Other metabolic hormones, especi- 



