. Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote. 458 CKUSTACEA. T- (Asellus) or they unite together into a common median penis which lies at the base of the abdomen (Oniscidce). A pair of styliform or complicated, hook-bearing appendages of the anterior abdominal feet are to be looked upon as accessory copulatory organs; in addition to these a pair of outwardly turned chitinous rods on the inner side of the second pair of feet may also be present (Oniscidce). The Cymothoidce are hermaphrodite * (Bullar), but the sexual organs become ripe
. Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote. 458 CKUSTACEA. T- (Asellus) or they unite together into a common median penis which lies at the base of the abdomen (Oniscidce). A pair of styliform or complicated, hook-bearing appendages of the anterior abdominal feet are to be looked upon as accessory copulatory organs; in addition to these a pair of outwardly turned chitinous rods on the inner side of the second pair of feet may also be present (Oniscidce). The Cymothoidce are hermaphrodite * (Bullar), but the sexual organs become ripe at different times. In the young stage these animals function as males, and possess three pairs of testes, two rudimentary ovaries internal to the testes, and a paired copulatory organ into which the two vasa deferentia a open (fig. 360). After a subse- quent ecdysis and after the fe- male glands have developed at the expense of the gradually diminishing male glands, the oostegites, which in the meantime have been developed, become free on the thoracic legs and the copu- latory organs are thrown off. Henceforward the animal func- tions only as a female. The embryonic development begins after the entry of the eggs into the brood pouch and is in- troduced by a centro-lecithal seg- mentation, the central part of the egg (food yolk) remaining at first unsegmented. The blasto- derm soon consists of a periphe- ral layer of naked nucleated cells and produces by a rapid growth of its constituent cells the ventrally placed germinal bands, at the anterior end of which the cephalic lobes are first marked off. The rudiments of the trifoliate appendages (dorsal organ) of the Isopod embryos are next formed as two prominences on the cephalic lobes. The physiological and morphological meaning of these structures has not yet been explained. Of the appendages the two pairs of antenna * J. Ilullar, " The generative organs of the Parasitic Isopoda," Jonrn. Anat. Pliysiol., 1S7G. P. Mayer
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