Text-book of comparative anatomy . EA—0 UTER ORGAN IS A TION 311 ally typically l)iramose, but appear in various ways transformed inconsequence of having undertaken the function of mastication. Itis always the basal joint of the protopodite, as that lying nearest themouth, which changes into a variously formed, hard, masticatoryportion (corpus mandibulare), and is often toothed on the side turnedtowards the mouth; the rest of the limb is more or less degenerated. Entomostraca.—In the Phyllopoda (Fig. 211, (?) the mandible is reduced to thehorny masticatory portion. The mandibles of the Ostraco
Text-book of comparative anatomy . EA—0 UTER ORGAN IS A TION 311 ally typically l)iramose, but appear in various ways transformed inconsequence of having undertaken the function of mastication. Itis always the basal joint of the protopodite, as that lying nearest themouth, which changes into a variously formed, hard, masticatoryportion (corpus mandibulare), and is often toothed on the side turnedtowards the mouth; the rest of the limb is more or less degenerated. Entomostraca.—In the Phyllopoda (Fig. 211, (?) the mandible is reduced to thehorny masticatory portion. The mandibles of the Ostracoda (IT) have retained thetypical form. The strongly developed masticatory joint is followed by a segmentedfeeler, whose first joint (corresponding with the distal joint of the protopodite)may carry a little fan-like plate. This represents the exopodite, while the feeler,with the exception of its first joint, represents the endopodite. The mandibles inthe free-living Copcpoda (E, F) are toothed masticators (hence Gnathostomata). Fin. -211.—Mandibles of various Crustaceans. A, Lucifer, Nauplius (after Brooks). E, Nebalia9 (after Glaus). C, Campylaspis nodulosa, Cumacean (after Sars). D, A larva of Branchipus, long (after Glaus). E, Notodelphys Almannii (after Thorell). F, Cyclops tenuicornis (). G, Apus lucasanus (after Packard). IF, Xestoleberis aurantia, Cytherid Ostracod (afterDahl). /, Astacus fluviatilis (after Huxley); 7, proximal, II, distal joint of the protopodite ; ex,exopodite ; en, endopodite (feeler); 1c, masticatory part or ridge. and carry feelers. The first joint of the feeler (2d joint of the protopodite) maycarry a segmented exopodite. In most parasitic forms the mandibles are changedinto stylet-shaped organs for sucking and piercing (Siphonostomata). Among theC impedes the mandibles are wanting in the RMzocephala, and in other groups aredeveloped as masticatory portions without feelers. Leptostraca (B) and Malacostraca (A, C, I).—The e
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanatomycomparative
