1. The intestine of Dysdercus is discontinuous in the larval instars, and urine from the Malpighian tubules is therefore uncontaminated by gut contents.
2. Excretion has been studied during the fifth instar, which lasts 8 days. Feeding only occurs in the first 4 days, during which there is a marked fall in water content. In the last part of the instar, when the animal only drinks, the water content returns to its original level.
3. The urine of Dysdercus is always liquid. There is a rapid rate of excretion during the first half of the instar, but when feeding ceases there is no further micturition and urine is retained in the rectum. Therefore there are two phases of excretion, designated excretory and post-excretory phases respectively.
4. The rectal epithelium is incapable of reabsorbing water against an osmotic gradient.
5. The urine which is retained in the rectum during the post-excretory phase acts as a water store; evaporative water loss is balanced by withdrawing water from this reservoir. During the excretory phase, a large volume of liquid is lost via the excretory system, but the loss is made good by drinking.