1. In Rhodnius larvae, when moulting is delayed under normal temperature conditions by exposure to high temperature directly after feeding, the brain is needed for a period longer than normal to complete development, i.e. the critical period is postponed.

2. This is associated with a delay in the activation of the thoracic glands and in the mitotic activity in the epidermis.

3. It is suggested that high temperature may act directly on the brain thus inhibiting the secretion of its hormone, although other possibilities are also discussed.

4. The process of wound heating at normal and high temperatures is compared. Injury of the integument results in the ‘activation’ of the epidermal cells and their migration towards the wound. Consequently, a zone of sparse cells is formed which persists at high temperature, since cell division in the epidermis is inhibited.

5. The bearing of the inhibition of cell division on the cessation of moulting at high temperature, even in the presence of the moulting hormone, is discussed.

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