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1. The reproductive cycle of the female fly was worked out at an average temperature of 24° C. The lowest egg of the right ovary develops first, and is ripe in 7 days. Ovulation never occurs earlier than the 8th day, and frequently later; it bears some relation to fertilization, for eggs in virgin females failed to ovulate for weeks. The first larva was produced in a variable time after fertilization (because of delayed ovulation), but the succeeding larvae were produced very regularly, with an average period of 9·9 days between them.
2. Pupae produced in the laboratory usually weigh less than those collected in the field. The reason for this is nutritional, and flies must take large meals at the right stage in gestation to produce large pupae. It is impossible to ensure that this happens with all flies in the laboratory.
3. Abortions are caused in captivity by flies obtaining too little blood. They may be induced in pregnant females by allowing them to take only small meals, when either an egg or a small larva is extruded. When these flies were properly fed later, they produced normal larvae.
4. A constant temperature of 30° C. causes sterility in females. Ovaries develop abnormally, embryos fail to hatch from eggs, but young larvae (in the uteri) are not adversely affected.
5. A constant temperature below 22° C. slows down the rate of development of the eggs in the ovaries and lengthens the larval period. Experiments at this temperature are complicated by inactivity of males, which leave many females unfertilized. The length of the combined embryonic and larval periods is 17½ days.
6. Experiments performed outside in the laboratory compound suggest that the period between each larva in the field (during December in Uganda) will be about 13½ days (min. temp. 16° C.; max. temp. 27° C.).
7. Flies appear to be able to breed equally well with relative humidities of 47, 88 and 100 per cent. In the drier air care must be taken with feeding, or the flies die from desiccation.
8. A temperature of 20° C. can cause pregnant females to retain their larvae for an extra 12 hours, but not longer.
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