138 KINETIC HORMONES — II 



4.214 Corpus allatum of Insecta possibly stimulated by a secretion 

 from the brain 



The corpora allata are ectodermal invaginations from the 1st 

 maxillary segment (§ 2.122) and their secretion inhibits metamor- 

 phosis in the nymphal or larval and pupal stages ; but it stimulates 

 egg-growth as wqW as increasing oxygen consumption in the adult. 

 The best evidence for any hormonal stimulation of their secretion 

 is derived from experiments on the blow-fly, Calliphora\ but the 

 results are not conclusive. 



If blow-flies, 8 hours after their emergence as adults, have 

 their median neurosecretory cells, m.n.c, removed from the brain, 

 it is found that the eggs in the ovary fail to mature, the result being 

 the same as that which follows allatectomy. Reimplantation of 

 mature corpora allata into allatectomized females can restore egg- 

 growth to normal in 93 per cent of cases ; but a similar implanta- 

 tion (of corpora allata) into flies deprived of m.n.c. has scarcely 

 any eflPect. The reimplantation of a double dose of m.n.c. into flies 

 deprived of their own m.n.c, but retaining their corpora allata did 

 not cause so great an increase in egg size as the reimplantation of 

 corpora allata into flies wdth normal m.n.c. (Thomsen, 1952). If 

 these results are interpreted as showing that the neurosecretion 

 from the brain has a stimulating effect upon secretion by the 

 corpus allatum, then they suggest that the brain cells secrete this 

 endocrinokinetic hormone less freely in isolated implants than 

 when they remain in situ in the brain. There is no positive evidence 

 that the brain has any control over the secretion of metabolic 

 hormones from the corpora allata; the effect of removing the 

 m.n.c. from the brain has not been tested in relation to oxygen 

 consumption. 



On the other hand it is clearly established that inhibition of 

 secretion from the corpora allata can be brought about by the brain, 

 both during metamorphosis (Part II, § 3) and while developing 

 eggs are present in the oviducts of the viviparous cockroach, 

 Leucophaea maderae (Liischer and Englemann, 1955). Growth of 

 the corpora allata, as well as their secretion, is released from this 

 inhibition by sectioning the nerves from the brain. Since this 

 operation not only deprives the corpora of nervous stimulation but 



