GROWTH 



85 



Rhodnius) which take only a single gigantic meal during each moult- 

 ing stage, so that the weight curve shows a series of acute peaks 

 gradually rising to a higher level (Fig. 12, C). 



Moulting 



The chief interest of insect growth centres round the phenomenon of 

 moulting or ecdysis. This is essentially a process of growth; for it is 

 the only means by which the hard parts can increase in size (p. 1). 

 There is no doubt, therefore, that growth is one factor that deter- 

 mines moulting. But in some insects (Tineola, Tenebrio) moulting can 

 occur repeatedly during starvation — and without any enlargement : 

 Tineola may sometimes develop a sort of 'moulting fever' and cast 

 the skin as many as eight times in two or three days; and adult 

 Thysanura will continue to moult without change in size or organiza- 

 tion. There must therefore be some other factor at work. This factor 



Time 



Time 



rSZ 



•ox 



fig. 12.— Growth curves; semischematic; A, Dixippus (modified after 

 Teissier); B, Gen is, Hem. (modified after Teissier); C, Rhodnius, 

 Hem. (modified after Buxton) 



The arrows indicate the time of moulting; the insect becomes adult at x 



