258 METABOLIC HORMONES 



receive capillaries from the carotid arteries (§ 5.322). The nervous 

 control of the secretion of oxytocin, w^hich is believed to stimulate 

 the excretion of salt, has not been estabHshed (§ 5.312); but it 

 might be expected from the fact that the secretion of oxytocin, 

 when it causes milk "let-down", is clearly under nervous 

 control and can be inhibited by anaesthesia (§ 3.114, Fig. 3-8). 

 This suggests that the release of the active chemical from a 

 neurosecretory cell is usually under nervous control ; but it is not 

 clear whether its own axon serves to transmit nerve impulses to the 

 distal point where secretion is released or whether some other 

 release mechanism is stimulated by impulses from the adjacent 

 neurones with which it remains in contact. 



5.523 Hormonal control of endocrine glands 



The remaining endocrine glands which secrete metabolic hor- 

 mones are all under some form of control by endocrinokinetic 

 hormones (§ 4.2). 



Among Crustacea, evidence is accumulating for the moult- 

 promoting hormone from the Y-organ being stimulated by an 

 endocrinokinetic hormone released from Hanstrom's sensory pore 

 organ (§ 4.211). There is well-established evidence in Insecta for 

 ecdysone, the morphogenetic moult-promoting hormone from 

 the prothoracic glands, being controlled by a neurosecretion from 

 the brain, acting as an endocrinokinetic hormone (§ 4.212). The 

 same prothoracotrophin may be expected to stimulate the release 

 of the antidiabetogenic hormone and the hormone which decreases 

 blood phosphates, which are released simultaneously with ecdysone 

 from the same glands, and are assumed to be identical with it. 

 Neither their identity nor the means of stimulating their secretion 

 has so far been established specifically. 



Control of the corpora allata of insects is less well understood 

 than that of the prothoracic glands. The formation and release of 

 their secretion is subject to inhibition by nerves from the brain; 

 their growth can be stimulated by a neurosecretion from the brain 

 (§ 4.213), passed to them via the store in the corpora cardiaca 

 (rather as the growth of the thyroid gland can be stimulated by 

 TSH) ; there are also indications that secretion of the hormone or 

 hormones from the corpora allata may be increased, if not solely 



