300 THE INVERTEBRATA 



reckoned to it, its maximum number of joints is five. These are found 

 on the thoracic limbs in the subclass Eucarida of the Malacostraca 

 as, for instance, in the crayfish, where they are named, in order from 

 the base outwards, the ischiopodite^ meropodtte, carpopodite, propodite, 

 and dactylopodite. 



In the subclass Peracarida, however, the five joints to which the above 

 names are usually given are not homologous with those so designated in the 

 Eucarida. Here the true carpopodite and propodite have fused, but the pre- 

 ischiopodite, which in the Eucarida is probably fused with the ischiopodite, 

 remains distinct, so that the distal part of the corm has still five joints. 



With the four possible joints of the protopodite these segments of 

 the endopodite make up a total of nine in the corm of the limb. 

 Sometimes a subdivision of certain of the joints into many jointlets 

 or annuli occurs. This may be seen in some of the thoracic limbs of 

 mysidacea and of certain prawns (Pandalus, etc.) and in many an- 

 tennae. A slender, many-jointed, terminal portion of either ramus 

 is known as a flagelliim. The exopodite is often unsegmented, but 

 when segmented usually possesses a flagellum. It does not possess a 

 standard number of joints. It is more often absent or reduced than is 

 the endopodite. 



The phyllopodium (Figs. 211 A, C, 213, 227), is a broader and flatter 

 limb than the majority of stenopodia. Its cuticle is usually thin, and 

 then the shape of the limb is maintained largely by the pressure of 

 blood within it. In these cases the flexibility is such that no joints are 

 needed. There is in this limb an axial portion or corm which bears on 

 the median side a row of lobes known as endites, and on the outer side 

 one or more lobes known as exiles. Of the latter the more distal, 

 standing usually opposite the third or fourth endite from the base and 

 often known as the flabelliim, is the homologue of the exopodite of the 

 biramous limb. Exites proximal to this are epipodites. That next to 

 the fliabellum is the hranchia (metepipodite) ; any which maybe present 

 proximal to the branchia are proepipodites (Fig. 227, pr.ep.). The 

 flabellum typically overhangs its attachment proximally as well as dis- 

 tally. In the latter direction it may extend so far as to form with the 

 distal part of the corm a pair of equal rami (Fig.211 C). The homology 

 of the endopodite then becomes apparent. This ramus corresponds to 

 that part of the corm of the phyllopodium which is distal to the 

 insertion of the flabellum or exopodite. Of the endites, that which 

 stands at the base of the limb is usually different in form from the 

 rest and used in one way or another for manipulating the food. It is 

 known as the gnathohase. The number of the endites varies. In the 

 Branchiopoda it is commonly six, but in the Anostraca (see p. 320) 

 there are indications of seven. It is greatest in the larval maxilla of 

 certain decapoda (Fig. 211 A), where it is nine, which, as we have 



