. Elementary text-book of zoology. Zoology. CRUSTACEA. 413 a morphologically to the eoxal joint of a limb, the following joints developing into a palp-like appendage (mandibular /"'//>). Then follow one or more pairs of weaker jaws (maxillce), and one or more pairs of maxillipeds, which more or less resemble the legs and, in parasitic forms, are often used for adhering (fig. 331). In parasitic forms, the upper and under lips not unfrequently give rise to a .suctorial proboscis, in which the styliform mandibles are placed. The appendages of the thorax, of which at least three pairs are
. Elementary text-book of zoology. Zoology. CRUSTACEA. 413 a morphologically to the eoxal joint of a limb, the following joints developing into a palp-like appendage (mandibular /"'//>). Then follow one or more pairs of weaker jaws (maxillce), and one or more pairs of maxillipeds, which more or less resemble the legs and, in parasitic forms, are often used for adhering (fig. 331). In parasitic forms, the upper and under lips not unfrequently give rise to a .suctorial proboscis, in which the styliform mandibles are placed. The appendages of the thorax, of which at least three pairs are present (Ostracoda), present an extremely various structure, in accordance with the mode of life and the use made of them. They are either broad leaf - shaped swimming feet (Phijllopoda], or bi- ramous appendages (Copepodci]; they may serve to produce currents in the water like the feet of the Cirripedia, or they may be used for crawling, walking, and running (Isopoda, Deca- poda}. In the latter case, some of them end with hooks or chelse. Finally the appendages of the abdomen, which frequently itself moves in toto and assists in locomotion, are either exclusively locornotory as jumping or swim- ming feet (Amphipoda), in which case they usually differ from the appendages of the thorax; or they serve with their appendages for respiration, as well as for carrying the eggs, and for copulation (Decapoda). The internal organization is not varied than is the external form. In the lower forms, the nervous system often consists of a ganglionic mass, which surrounds the oesophagus and is not further. FIG. 331.—Young stage (larva) f the Lobster (after G' 0. Sars). a, The lurva seen from tlie side ; -ff, ros- trum ; A', A", antennae; Ef" third maxilliped; /•", anterior ambulatory leg. I, mandible with palp; c. anterior maxilla with two blades and palp; •', pos- terior maxilla with vibratile plate (scaphognathite); e, first,/, second Please note that
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1884
