. A manual of zoology. Zoology. IV. INSECTA: HEXAPODA 413 ing an irritating substance (cantharidin) through the Jointing memljranes of the legs as a means of defense. Tlie Hexapoda are dioecious. The paired gonads consist of a few or many ovarial or testicular tubules (fig. 454), in the abdomen. Their paired ducts (oviducts, vasa deferentia) open separately in the Ephemerida and young Apterygota, but all other Hexapoda have a single ventral un- paired sexual opening just in front of the anus. This arises as a median invagination of the ectoderm (hence lined with chitin), which extends inwards
. A manual of zoology. Zoology. IV. INSECTA: HEXAPODA 413 ing an irritating substance (cantharidin) through the Jointing memljranes of the legs as a means of defense. Tlie Hexapoda are dioecious. The paired gonads consist of a few or many ovarial or testicular tubules (fig. 454), in the abdomen. Their paired ducts (oviducts, vasa deferentia) open separately in the Ephemerida and young Apterygota, but all other Hexapoda have a single ventral un- paired sexual opening just in front of the anus. This arises as a median invagination of the ectoderm (hence lined with chitin), which extends inwards and meets the genital ducts (modified nephridia). The re- ceptaculum seminis, a sac connected with the female genitalia, has a special biological in- terest. In insects which copulate but once during life it retains the spermatozoa for a long time (four years in bees) in a living con- dition. As the eggs are laid they may be impregnated by spermatozoa from it. Since a firm shell or diorion is developed around the egg in the ovary, entrance of spermatozoa is only possible by a micropylar apparatus, a system of tubes penetrating the chorion at one end of the Fig. 4^S-- -Ventral view sac; d, poison giand; g, its duct; ga, teriTiinal ganglion, beside it accessory gland; I, stylet; 2, groove of sting (black); 3, sheath of sting; I, angle piece; II, quadrate plate for attachment of muscles. Oviposition occurs in many insects by means of °f ^''"S of bee (after Packard an ovipositor which may be developed in two ways. â ^"'^ Cheshire). _ W,_ poison In beetles, flies and butterflies the last somites of the body are small, and are normally retracted into the body but can be protruded as a long tube for oviposition. In Hymenoptera, Hemiptcra, Orthop- tera and dragonflies the ovipositor (tercbra) is formed by special appendages, the gonapophyses, four to six in number, which arise from the ventral side of the eighth and ninth abdominal segments. In the Orthoptera two pa
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectzoology, bookyear1912
