132 KINETIC HORMONES — II 



either trophic or tropic especially in such compound names as 

 gonadotrophic ; but reasons have already been given (§ 1.51) for 

 avoiding the confusion to which the use of these terms leads. 



It is not all endocrine glands, the secretion of which can be 

 stimulated by hormones ; but the exceptions are clear cut, at least 

 in vertebrates. Glands formed from modified nerve cells are never 

 so controlled, nor are the parathyroids and the insulin-secreting 

 cells of the islets of Langerhans in the pancreas (§ 5.52); such 

 control is very rare for any gland secreting kinetic hormones. It is 

 almost always the glands secreting hormones with metabolic or 

 morphogenetic actions, or both, that are controlled by endocrino- 

 kinetic hormones. Among invertebrates, the only cases so far 

 known are glands derived from the ectoderm; but it seems more 

 than likely that some will be found in the gonads. The vas deferens 

 gland of Crustacea, with its morphogenetic hormone, could well 

 be controlled by such a hormone ; but neither this nor any other 

 form of control has yet been found for it. Among vertebrates, all 

 the endocrine glands in question are derived either from the 

 endoderm or the mesoderm, and all are controlled by endocrino- 

 kinetic hormones from the adenohypophysis. 



The action of an endocrinokinetic hormone is much more 

 difficult to establish than that of a hormone which acts directly 

 upon some kinetic or metabolic process, especially as it is so often 

 found that the endocrinokinetic hormone stimulates a whole 

 complex of metabolic processes, interference with any one of 

 which may upset the balance of the rest, and interfere with the 

 health and reactions of the test animal. An indication of the 

 minimum number of experiments that are theoretically necessary 

 to establish the interrelations of two hormones, one endocrino- 

 kinetic and one metabolic, has already been given (§ 1.6). It is rare 

 to find animals in which the nervous system does not introduce 

 further complexities. Often the dilTerent stages in the experimental 

 proof have been supplied by different authors, and can only be 

 interpreted by reference to the histological and chemical results of 

 yet other workers. Interpretation of work upon vertebrates has 

 been particularly beset by difficulties introduced by testing the 

 hormones from one class of animals upon those of another. 



In the cases given below, the main action of each endocrine- 



