Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote elementarytextbo01clau Year: 1892-1893 DERMAPHIIODITISM. 99 eggs or of the developing embryos (uterus). Their terminal section presents differentiations subserving fertilization (receptaculmn seminis, vagina, copulatory pouch, external generative organs). The efferent ducts of the testis, the vasa deferentia, likewise frequently give rise to reservoirs (vesicular seminales) and receive glands (pros- tate), the secretion of which mixes with the sperm fluid or surrounds aggregations of the spe
Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote elementarytextbo01clau Year: 1892-1893 DERMAPHIIODITISM. 99 eggs or of the developing embryos (uterus). Their terminal section presents differentiations subserving fertilization (receptaculmn seminis, vagina, copulatory pouch, external generative organs). The efferent ducts of the testis, the vasa deferentia, likewise frequently give rise to reservoirs (vesicular seminales) and receive glands (pros- tate), the secretion of which mixes with the sperm fluid or surrounds aggregations of the spermatozoa with a firm sheath (spermatophors). The terminal section of the vas deferens becomes exceedingly muscular, and gives rise to a ductus ejaculatorius, which, as a rule, is accompanied by an external organ of copulation to facilitate the conveyance of the semen into the female generative organs. The generative organs present either a radial (Coeienterata, Echinodermata) or a bilate- rally symmetrical arrangement (fig. 91), a contrast which is visible in the typical arrange- ment of all the systems of organs. The simplest and most primitive condition of the generative organs is the her- maphrodite. Ova and sper- matozoa are produced in the body of one and the same individual, which thus unites in itself all the conditions necessary for the preservation of the species, and alone represents the species. Instances of hermaphroditism are found in every group of the animal kingdom. But they are especially nume- rous in the lower groups, and also in animals in which the movements are slow (Land-snails, Flat-worms, Hirudinea, Oligochoeta), or which live singly (Cestoda, Trematoda), or in attached animals which are without power of changing their position (Cirripedia, Tunicata, Bryozoa, Oysters). The hermaphrodite arrangement of the gene- rative organs presents great variation, which, to a certain extent, forms a gradual series tending towards the separation of the sexes. In the s
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