On the Genital System of Lyctus brunneus Steph., with a Note on Lyctus linearis Goeze (Coleoptera).

Abstract

Both sexes in L. brunneus are sexually mature when they have emerged through the wood from their pupal chambers. An external sex-character is described. In the male the reproductive organs consist of two testes of twelve pyriform testicular follicles of unequal size, six arising from each convoluted vas deferens, which terminate in a pair of jointed subcylindrical seminal vesicles. A short tube arises from each seminal vesicle, and forms the ejaculatory duct which empties into the cedeacrus. Partly superimposed over the seminal vesicles and emptying into the short tubes are the paired accessory glands. They are subcylindrical, slightly tapering, and are curved around to underneath the ejaculatory duct. There is a pair of pygidial glands. In the female the reproductive organs consist of two ovaries, each composed of fourteen ovarian tubes with the nutritive cells situated at their apices. The ripe eggs accumulate in a calyx which continues to form the oviduct. The oviducts terminate in a chitinized setsæ-lined paired valve which forms the source of the common oviduct. At this point the voluminous spermatheca arises; it terminates in a tubular spermathecal or accessory gland. The common oviduct disappears into the invaginated double tubular “ovipositor” at a point in the metathorax, where the rectum also enters. In the testicular follicles the spermatozoa are in bundles, in the spermatheca they are in packets or spermatophores. The “ovipositor” has been found to consist of a double tubular prolongation of the ninth abdominal segment, with a reduced tenth segment towards the apex. When extruded the “ovipositor” is approximately the length of the beetle. Situated at the apex of the “ovipositor” are the genitalia with the anus a short distance behind. Arising as an invagination of the eighth sternite and extending into the metathorax is the long, flexible, and strongly-chitinized cloacal stalk, from which arise systems of muscles for exserting and withdrawing the ovipositor. These muscles are found to lie modified intersegmental muscles. Morphologically the gonopore in both sexes was found to arise medianly on the ninth sternite, and the homology of the genitalia appears. In the larva of L. brunneus there are nine pairs of spiracles, one thoracic and eight abdominal; in the adult there are also nine pairs, two thoracic and seven abdominal. The movement which the rectum of the female is subjected to has been observed to be injurious to this organ, in that, lacking any musculatory system for its withdrawal, other than its muscular structure, it was found convoluted inside the “ovipositor” of an eg-laying specimen. This defectiveness must accelerate death.