The structure and function of the bursa copulatrix of the monarch butterfly (Danaus plexippus)

The bursa compulatrix of the Monarch butterfly was investigated utilizing light microscopy, histochemistry, and scanning and transmission electron microscopy in order to relate its morphology to the release of sperm from the spermatophore. The bursa has a row of large chitinous teeth on either side of the organ. The dorsal and ventral surfaces are covered with chitinous plates, the plates having bristles on one side. A single layer of cells lies under both the plates and teeth, one columnar cell under each plate, one cuboidal cell under each tooth. The toothed area has no muscle cells. However, the dorsal and ventral hemispheres of the bursa each have a crescent-shaped packet of muscle fibers that traverse the organ; there are no longitudinal fibers. Spermatophores with thick walls were found in the bursal lumen. Morphological evidence suggests that the presence of the spermatophores is sensed by the bristles and that the packets are opened by contraction of the muscles bringing the large teeth into contact with the spermatophore wall.