136 KINETIC HORMONES — II 



and Bombyx are the only ones that need to be referred to here. 

 These glands have all been found to secrete the moult-promoting 

 hormone, ecdysone, in response to an endocrinokinetic hormone, 

 PROTHORACOTROPHIN, from the neurosecretory cells in the inter- 

 cerebrum of the brain. 



It is clearly established that no nervous connection is needed 

 between the brain and prothoracic glands for stimulation to be 

 effective, except possibly in the Diptera. A conclusive proof for 

 the action of an endocrinokinetic hormone in the Lepidoptera can 

 be given in connection with the termination of diapause (§ 5.1 12\ 

 and is therefore more appropriate here than an example derived 

 from the control of moulting (Part II, § 3); but the interaction of 

 the hormones seems to be the same in either case. 



In nature, diapause of the Cecropia silkworm, Hyalophora^ lasts 

 for 6 to 7 winter months before the tissues again become active 

 and differentiation leads to the emergence of the adult in the 

 spring (§5.12). Diapause can be shortened or "broken" artificially 

 in various ways, of which the simplest is the injection of an active 

 extract of ecdysone from the prothoracic glands. These glands do 

 not secrete during diapause, but they can be induced to do so at 

 any time by the presence of an actively secreting brain. Reactiva- 

 tion of a diapausing brain can best be brought about by chilling it 

 suitably (Williams, 1952). If a diapausing pupa is joined by a 

 plastic tube to a diapausing pupal abdomen, so that their influence 

 on each other can only be by hormones in circulating haemolymph, 

 then a chilled brain, implanted in the hinder abdomen (Fig. 4-6), 

 breaks diapause in the anterior specimen first, and only later in the 

 hinder abdomen, where the implant is. It may be concluded that 

 the brain has no direct effect in the hinder abdomen, but that its 

 endocrinokinetic hormone, prothoracotrophin, stimulates the 

 prothoracic glands in the anterior specimen to secrete ecdysone, 

 which may override the diapause hormone, D (see § 5.112). If the 

 length of the tube separating the two pupae is increased, the time 

 lapse between brain implantation and the end of diapause is also 

 increased. 



The possibility that the secretion of other metabolic hormones 

 by the prothoracic gland may also be subject to endocrinokinetic 

 stimulation by a hormone from the brain has not, apparently, 



