. Elementary text-book of zoology, general part and special part: protozoa to insecta. Animals. TnORACOSTEACA. 463 of biramous swimming feet, which arise from the three posterior free segments of the thorax. The thoracic legs are either, at least in part, biramous (with summing ramus), or as in the Decapods the exopodite is absent and the legs have the form of ambulatory appendages. They then terminate with simple claws; the anterior frequently with lai-ge chelae. The terminal joints may however be broad plates, in Avhich case they can be used as swimming feet. The biramous legs of the sixth a
. Elementary text-book of zoology, general part and special part: protozoa to insecta. Animals. TnORACOSTEACA. 463 of biramous swimming feet, which arise from the three posterior free segments of the thorax. The thoracic legs are either, at least in part, biramous (with summing ramus), or as in the Decapods the exopodite is absent and the legs have the form of ambulatory appendages. They then terminate with simple claws; the anterior frequently with lai-ge chelae. The terminal joints may however be broad plates, in Avhich case they can be used as swimming feet. The biramous legs of the sixth abdominal segment are, as a rule, broad and fin-like and form, together \vith the last abdominal segment Avhich is transformed into a large plate (telson), the caudal fin. The feet of the five anterior abdominal segments, on the other hand, are sometimes swimming feet {Stomatopoda), sometimes serve to carry the eggs, or the anterior may assist in copulation (in the male). They may however be more or less rudimentary and some of them absent. "With rare excep- tions [Mysidce) all the Thoracostraca possess gills, which are either tufted or composed of regular lancet-shaped leaves. The gills are appen- dages of the limbs: in the Stomator)oda , ii 1 J J. ^'°- Sl^a.—Cephalothorax of Agfacusjluviafilie, after removal they are attached to of the branchiostegite (after Huxley). K, Gills; S, ros- the abdominal feet in ^"^^ > ^' stalked eye; Mp, scaphognathite (of the second ' maxilla); Mxf", third maxilliped. the Scliizopoda and Decapoda to the maxillipeds and ambulatory feet. The Cumacea are -without gills, except for a single pair on the second pair of maxil- lipeds. In the Decapods they are contained in a special branchial chamber beneath lateral expansions of the carapace (bi-anchiostegite) (fig. 363). The organs of circulation also attain a high degi^ee of development, the highest not only among the Crustacea, but in general amongst all Arthropods. A heart and ve
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanimals, bookyear1892
