REVERSAL OF SEX PRODUCTION IN MICROMALTHUS

¹ From Union College, Schenectady, N. Y. and the Marine Biological Laboratory, Woods Hole, Mass.

1. The paedogenetic, arrhenotkous female in the beetle, Micromalthus debilis (Leconte), gives birth to but one male embryo, although unshed males also develop.

2. Factors which determine this uniparity are still uncertain, but neither greater age nor more favorable position in the mother are determining factors.

3. When the single successful male offspring is not allowed to devour his mother, a new crop of eggs develops in the ovary.

4. These new eggs are all of the elongate female type. They develop into a larva identical in appearance with the first stage larva of the thelytokous paedogenetic female.

5. Histologically the new eggs originate from undeveloped ovarioles which failed to develop during the first period of growth of the male-producing eggs.

6. Sex of brood in Micromalthus is obviously determined by environment, intrinsic or extrinsic, and not by the hereditary constitution of the mother.