. Elementary text-book of zoology. Zoology. AMPHIPODA. 451 organ. Appendages of the leg> may also be present as additional aids to copulation. The mature ova are, as a rule, carried about by the female in brood pouches formed by the lamellar appendages of the thoracic feet (oosteyites}. Development as a rule takes place without metamorphosis, but the form and appendages of the young animal not unfrequently differ from those of the adult animal (Phronima). The segments and the appendages may even, be incom- plete in number after birth (Isopoda). Fossil Arthrostraca are found in the Oolite (A
. Elementary text-book of zoology. Zoology. AMPHIPODA. 451 organ. Appendages of the leg> may also be present as additional aids to copulation. The mature ova are, as a rule, carried about by the female in brood pouches formed by the lamellar appendages of the thoracic feet (oosteyites}. Development as a rule takes place without metamorphosis, but the form and appendages of the young animal not unfrequently differ from those of the adult animal (Phronima). The segments and the appendages may even, be incom- plete in number after birth (Isopoda). Fossil Arthrostraca are found in the Oolite (Archceoniscus). Pro- soponisci's occurs in the Permian, Amphipeltis in the Devonian. 1. Sub-order.—Amphipoda.* Arthrostraca v:ith laterally compressed bod//, with gills on the thoracic feet and an elongated abdomen, of which the three anterior segments bear the swimming feet, while the three posterior bear posteriori// di- rected feet adapted for sjtriitt/iit;/ (fig. 356). The .1 i/tph ipoda are small animals, being only in rare case> several inches long (Lysianassa magellanica). They move in the water principally by spring- ing and by swim- ming. The head, which is sometimes small (Crevettina, fig. 356), sometimes large and then much swollen (Hyperina, fig. 357). is sharply distinct from the thorax and is fused with the first of the seven thoracic segments only in the aberrant group of the Lcemodipoda. The two pairs of antenna? usually consist of a short strong shaft * Besides the older works of. De Geer. Riisel, M. Edwards, compare C. Speuce Bate, •' On the Morphology of some Amphipoda of the Division Hyper- ina," Ann. of Xaf. Ser. 2. vol. 1857. C. Spence Bate. •• On the uidincation of Crustacea," Ann. of Nut. H/xt., Ser. 3. vol. i. C. Spence , " Catalogue of the specimens of Amphipodous Crustacea in the collect i«>n of the British ; London. 1802. E. van Beneden et Em Bessels. •' Memoire sur la formation du Bl
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1884
