. Elementary text-book of zoology. Zoology. isoroDA. 457 Lrl they bear two fiagella. in the Amphipoda, pale, plumous setse and olfactory cones are present on the antenna-. The mouth parts are in some parasitic Isopoda modified for piercing and sucking. The mandibles (except in Boj)yridw and Oniscidce) often bear a- three- jointed palp. On the other hand, the two pairs of maxilla?, which are usually bi- or tri-lobed, are in general without the palpiform appendage. The maxillipeds form a sort of underlip, but present great differences in the arrangement of their parts (fig. 358). As a rule t
. Elementary text-book of zoology. Zoology. isoroDA. 457 Lrl they bear two fiagella. in the Amphipoda, pale, plumous setse and olfactory cones are present on the antenna-. The mouth parts are in some parasitic Isopoda modified for piercing and sucking. The mandibles (except in Boj)yridw and Oniscidce) often bear a- three- jointed palp. On the other hand, the two pairs of maxilla?, which are usually bi- or tri-lobed, are in general without the palpiform appendage. The maxillipeds form a sort of underlip, but present great differences in the arrangement of their parts (fig. 358). As a rule the seven pairs of thoracic legs are adapted for walking or attachment, and in the female some of them are provided with delicate membranous plates (oostegites) which form a brood pouch. They never bear gills. The branchial function is dis- charged by the delicate inter- nal rami or endopodites of the abdominal limbs (pleo- pods), the anterior pair of which is • frequently modified to form a large operculum overlying the following In certain of the terrestrial Isopods (Porcellio and Arma- dillo] the opercular plates of the two anterior pairs of abdominal limbs contain a system of air spaces which ap- pear to assist respiration. The heart, unlike that in Amphi- pods, lies (except in Tandidce) in the posterior thoracic seg- ments or in the abdomen. The sexes are (except in Cymotfioidoe) separate, and the position and arrangement of the generative organs correspond in general with those of the Amphipoda. The sexes are distinguished In- external sexual characters, which in some cases (]joj>t/ri</«') may lead to a strongly-marked dimorphism (fig. 359, a, b). In the male three tubular testes unite on either side to form a dilated seminal vesicle, from which the vasa deferentia are given oflf. The latter are frequently separate along their whole length and, at the end of the last thoracic segment, each of them enters a cylindrical appendage. FIG. 359.—Gyge branchiali
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1884
