336 THE INVERTEBRATA 



but in most cases the endopodite is the larger, and forms with the 

 protopodite an axis, the corm^ on which the exopodite stands laterally 

 (Figs. 222 E, F, 223, 286). In a few instances the exopodite is the 

 larger. 



The protopodite most often has two joints, a proximal coxopodite 

 and a distal basipodite. In certain cases, however (as in the antenna 

 of the Mysidacea and Asellus, the last three thoracic limbs of the 

 Stomatopoda, certain swimming limbs of the Branchiura (Fig. 254 B), 

 and less clearly in many other instances), a basal joint, the precoxa or 

 pleuropodite, precedes the coxopodite; moreover the basipodite may 

 be divided into two joints — the probasipodite, which then usually bears 

 the exopodite, and the metabasipodite or preischiopodite . This con- 

 dition is seen most clearly on the thorax of the malacostracan genera 

 Anaspides and Nebalia (Fig. 222 E), where the two components of the 

 basipodite are separate in some limbs and fused in others; it is less 

 obvious in other cases in which it occurs. Thus the full possible 

 number of joints in the protopodite is four. Some authorities, how- 

 ever, prefer to regard the preischium as part of the endopodite, in 

 which case the true protopodite has only three joints at the most. 

 Epipodites, when they are present, are borne upon the precoxa 

 (proepipodites) or coxopodite (fnetepipodites). 



The endopodite is usually segmented. If the preischium be not 

 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 , meropodite^ 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. Some- 

 times 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 3. flagellum . 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. 222 A, C, 224, 238), is a broader and flatter 

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



