1. Inorganic excretion has been studied during both phases of excretion.
2. Large amounts of potassium, magnesium and phosphate are excreted during the first phase, but sodium and chloride losses are reduced to a minimum.
3. There is a close correlation between inorganic excretion and the relative abundance of these ions in the diet.
4. The inorganic ion and total nitrogen content of the urine retained in the rectum during the post-excretory phase shows little change. This provides strong evidence for assuming that the Malpighian tubules are inactive during this period.
5. Magnesium, potassium and calcium concentrations in the haemolymph remain relatively constant; sodium and chloride concentrations, however, show a marked increase during the middle of the instar. Amino acid concentration compensates for these changes, so ensuring a constant osmotic pressure in the haemolymph.
6. The high rate of liquid excretion in Dysdercus probably results from an excessive intake of inorganic ions.