1. A method has been developed for obtaining 200-300 flies daily from a culture of Protophormia terrae-novae reared on whale-meat.

2. Normal growth changes in adults have been described, and five stages in ovarial development have been denned.

3. Experimental conditions affecting ovarial growth in adults have been investigated and a satisfactory routine method for examining the effect of adult nutrition on ovarial growth has been devised. Precautions were taken against bacterial contamination of food although non-sterile conditions were used.

4. Ovarial development was not related to relative humidity, if above 55% R.H., nor to the weight of the adults at emergence.

5. Evidence has been given for the conversion of food material from pupal to adult fat body and for the transfer of material from fat body to ovaries at yolk formation.

6. Healthy adult females can be maintained on a diet of sucrose and water. Addition to the diet of protein or amino-acids produces only slight enlargement of the ovaries. Yolk formation only occurs if the diet is further supplemented by accessory factors, or substances required only in small amount. Ovarial maturation requires considerable amounts of protein, though not more than 0.4 mg. per fly is needed and food solutions must be concentrated. The accessory factors have not been identified but are known to be resistant to slow boiling and are dialysable. Certain mineral salts and B vitamins are thought to be involved.

7. Tryptophane is an essential part of the amino-acid mixture.

8. Protein hydrolysates or equivalent amino-acid mixtures can be substituted for the whole protein but are less effective. The proportions of amino-acids present are very critical, particularly when the amino-acids are in a free state. The amino-acid mixtures have no toxic effect and the presence of some D-isomers do not inhibit growth, although some D-isomers cannot be used by the flies for growth.

9. A chemically defined diet similar to that used for Drosophila did not promote ovarial growth in Protophormia. A mixture containing ten B vitamins, ribose nucleic acid and mineral salts and cholesterol contained some effective accessory substances but lacked some unidentified factor required for yolk formation. The missing factor was not vitamin B12. Penicillin had no significant effect on ovarial growth whether used in minute or in antibiotic concentration.

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