1. Methods used in the production of pupae of G. morsitans, Westw., in the laboratory have been described.

2. Observations, based on the pupae produced in the laboratory, have been recorded on larviposition, pupation, pupal period and stages of pupal development.

3. The pupal period was found to vary with the temperature, from 23·1 days when kept constantly at 86°F., to 48·5 days at a varying temperature, the mean noon temperature during development being 70·0°F.

4. Examination of puparia collected from natural breeding-sites showed that there is a fairly heavy mortality in the pupal stages in nature, amounting in some cases to as much as 50%.

5. Parasitisation by the Hymenopterous parasite, Syntomosphyrum glossinae, was found to a very slight degree—0·2& only.

6. Heavier parasitisation by three species of Bombyliids—Thyridanthrax abruptus, T. lineus, and T. argentifrons—occurred.

7. The living, dead, and parasitised puparia could be distinguished by (a) immersion in methylated spirit of S.G. 0·820, when those sinking would be alive, and (b) subsequent immersion in petrol of those floating in methylated spirit, when those sinking would for the greater part be parasitised and those floating would be dead.

8. The degree of temperature lethal to pupae was found to depend on duration of exposure. Thus, whereas pupae survived exposure to 55–57°C. for 2 minutes, 45–50°C. was lethal when the exposure lasted half an hour, whilst even 40°C. was lethal when continued for 4 hours or more, and pupae failed to survive 13 days at 35°C.