It had been noted by Plagge (1938) that although the implanted brain would cause pupation in Deilephila larvae from which the brain had been removed, it would not induce pupation in the posterior fragments of ligated larvae. The significance of this was proved experimentally by Willians (1947) who repeated the experiment on the diapause pupa of Platysamia. A chilled brain implanted in the isolated abdomen of the pupa in diapause will not induce development, whereas it will cause development of the anterior half from which the brain has been removed. On the other hand, the isolated abdomen will develop if it is provided with a chilled brain plus prothoracic glands.
As in Rhodnius, the actual source of the secretion in the brain is the neurosecretory cells. But if chains of decapitated pupae are employed and a chilled brain is implanted into the first member, development is renewed in the entire series, which may be as much as 24 cm in length.
The Physiology of Insect Metamorphosis
V. B. Wigglesworth