A PRELIMINARY HISTOLOGICAL STUDY OF THE INSEMINATION REACTION IN DROSOPHILA GIBBEROSA

¹ Division of Entomology and Economic Zoology, University of Minnesota

1. Macroscopic features and microscopic structure of vaginae of Drosophila gibberosa Patterson and Mainland are described in virgin females, mated females, females with testes injection, male accessory gland injection, testes plus male accessory gland injection, whole male brei injection, 2 per cent gelatin injection, saline injection and 2 per cent NaCl injection.

2. The wall of the vagina consists of intima or cuticle, epithelium and muscle layers.

3. The insemination reaction occurs in vaginae of mated females, females with testes injections, and testes plus male accessory glands injections. The reaction consists of five characteristic features: (a) increase of size of vagina, (b) increase of volume of epithelial cells, (c) presence of reaction mass, (d) dense appearance of nuclei, and (e) more heavily stained cytoplasm. Some but not all of these features have been produced separately by artificial insemination with experimental solutions.

4. The increase in volume of the vaginal epithelial cells is compared with the known increase in volume of epidermal cells during deposition of a new cuticle.

5. Cell volumes can be altered by the injection of hypertonic and hypotonic saline solutions as shown by both volume and intensity of staining.

6. The reaction of vaginae of mated females reaches its maximal distention two and a half to four hours after mating. Then it decreases in size gradually and returns to its normal size five or six hours after mating.

7. The reaction mass within the vagina is composed of spermatozoa and substances of acidophilic staining property. The increase and decrease of the size of the reaction mass during the course of the reaction keeps well in pace with the size of the vagina.

8. The insemination reaction of vagina as demonstrated by Patterson (1947) seems not induced by spermatozoa, and the present data show that it is not induced by male accessory glands either. Since the semen of Drosophila consists of secretion of accessory glands, spermatozoa and some substances from testes besides spermatozoa, it is suggested that the agent which induced the insemination reaction is most likely some factor from the testes other than the spermatozoa.