11. Neither the eggs of Hemiptera or of other insects arise through the agency of “oöblasts,” but like the epithelial and nutritive cells arise by a gradual differentiation from the indifferent elements of the ovarian tubes.
12. The different elements of the egg-tubes, also the eggs, have the morphological value of cells.
Origin of incipient eggs in the germ of the testes.—Heymons has detected in the germ of the testes of the male larvæ of Phyllodromia germanica 7 mm. in length, young or incipient eggs, similar to those seen in the ovarian tubes of the female larva of the same size. In another male larva of the same size also occurred short cylindrical tubes each with a terminal thread, which had the appearance of rudimentary egg-tubes. Hence he thinks that every part of the genital germs (Anlagen) in the male, which are not concerned in the formation of testicular follicles, represents the germ of a female genital gland. As is well known, no insects are hermaphroditic, but this case of the practical origin of eggs and egg-tubes in the lowest division of the male efferent passage, which is homologous with the egg-producing division of the female ovarian tubes, points back to hermaphroditic ancestors. And Heymons suggests that the frequent occurrence of hermaphroditism in insects probably confirms this view.
Fig. 479.—Abdomen of queen bee, under side, × 8: P, petiole; o, o, ovaries; hs, position filled by honey-sac; ds, place through which the digestive canal passes; od, oviduct; co.d, common oviduct; E, egg passing oviduct; s, spermatheca; i, intestine: pb, poison-bag; p.g, poison-gland; st, sting; p, palpi. B, vestigial ovaries of ordinary worker; sp, vestigial spermatheca. C, partially developed ovaries of fertile worker; sp, vestigial spermatheca.—After Cheshire.
The bursa copulatrix.—The copulatory pouch in most insects is a special cup-shaped appendage of the vagina adapted for the reception of the male organ during sexual union. Its mode of formation in the cockroach is thus described by Haase:—
“By the retreat of the female sexual aperture, situated in the 8th ventral plate, a considerable space, the genital pouch, is produced; this is formed chiefly by the extended connective membrane between the elongated 7th and 8th ventral plates. This serves for the development of the egg-cocoon, which is retained by the internal appendages of the posterior gonapophyses.”
The fertilization of the female takes place once for all a long time previous to oviposition; the semen in the receptaculum seminis passes out as the eggs slip down the egg-passage, and a spermatozoön gains entrance into the interior of the egg through the micropyle. In Œcanthus, according to Ayers, fecundation probably takes place while the egg is passing into the vagina, “since it is hardly possible that the male element could gain access to the follicles before the chorion is secreted.”
In the Lepidoptera, as has been stated, the copulatory pouch opens separately from the opening of the oviduct (vagina), but a slender canal connects the pouch with the vagina (Fig. 310, bc). The outlet (“vagina” of Burgess) of the copulatory pouch opens between the 7th and 8th segments, that of the oviduct (vagina) on the 9th segment being “situated immediately below the anus and hardly separated from it, between the lappets of the 9th segment.” (Burgess.) The opening of the copulatory pouch is, as we have seen, the genuine or primitive sexual opening.
