1. The effects of prolonged fasting on the epidermal cells, ventral abdominal muscles and fat body of Rhodnius 4th-stage larvae are described. Ribonucleic acid (RNA) almost disappears from nucleolus and cytoplasm, and the mitochondria are reduced in numbers. Dark osmiophil deposits, believed to be breakdown products of mitochondria, appear in the cytoplasm.

2. The effects of nutrition, distension, and moulting hormone were studied on these three tissues after starvation.

3. Nutrition alone has little effect on the epidermal cells and ventral muscles; but nutrition plus moulting hormone at once restores their capacity for protein synthesis and growth, as shown by the enlargement of the nucleoli, the appearance of RNA in the cytoplasm, and a great increase in the mitochondria. This general effect is termed ‘activation’; it leads on to cuticle formation and moulting.

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