184 METABOLIC HORMONES 



of diapause eggs in 70 per cent of cases. This effect can, in 

 fact, be produced by ganglia from males as well as females, 

 and even from moths of other species, including Antheraea 

 pernyi (which does not itself lay diapause eggs but has a 

 so-called "pupal diapause"; Lees, 1955). 



These experiments have been substantiated by extraction of 

 pure diapause hormone from the suboesophageal ganglia of 

 Bombyx (Hasegawa, 1957). 



Another very unusual feature has been postulated for the 

 hormones concerned with diapause in Bombyx (Hinton, 1953). 

 Since the adults are apparently unaffected by the diapause hormone 

 which they secrete, and the eggs they lay continue to develop for 

 over a day before the hormone D acts upon them, it is suggested 

 that the moult-promoting hormone, ecdysone (Part II, § 3), 

 from the prothoracic glands, in some way protects the tissues of the 

 adults from the action of the diapause hormone, present at the 

 same time. Moreover, some ecdysone must be passed into the eggs 

 with D before they are laid, and this postpones the onset of dia- 

 pause. It is assumed that ecdysone is broken down in a few hours 

 in the young embryo, whereas the break-down of D is extremely 

 slow, so that diapause lasts until the following spring when the 

 supply of D is eventually eUminated. This might also be true for 

 the embryos of Locustana pardalina, in which diapause ends and 

 growth begins again before any organized endocrine glands have 

 developed (Jones, 1956). 



In the Cecropia silkworm, Hyalophora^ the climatic determina- 

 tion of diapause acts on the late embryo or early larva, which, 

 unlike that of Bombyx^ itself undergoes diapause some months 

 later in the pupal stage, when the suboesophageal ganglion is 

 already well developed. Hinton (1953) maintains that the hormone 

 D is again responsible for causing diapause ; but others, especially 

 Williams (1952), claim that it is due to the lack of the prothoracic 

 HORMONE, rather than to the presence of an inhibitor, D, acting 

 on the brain. The somewhat scanty evidence can be interpreted 

 either way. It is agreed that the end of diapause is due to the 

 re-activation of the prothoracic glands. This is due to renewed 

 neurosecretion of prothoracotrophin from the brain (§4.211), 



