HIGHER CRUSTACEANS (MALACOsI KACAi 831 



the body is distinctly divided into two parts: the iinlerior, ihonuc 

 or trunk {th), comprising the first eight somites; the iKJstcn t. 

 abdomen {ahd), with the six following (to which the teiM>n is ad.l. 1 . 



The appendages of the thorax are called thoracic limbs. Some 

 or all of the first three of them are in many cases s|Hiiali/.« .' 

 maxilHpeds (maxp), and in this case the following live are i.: ^ 

 peraeopods (perp). The abdominal appendages are ailled plct>|xxls 

 (pip), but those of the last (sixth) pair are often difTerentialetl m a 

 peculiar way, so as to form with the telson a taudal fan. and in 

 this case the name uropods (urp) is used for them. 



The detail-structure of the appendages of the dilTerent re;,aons 

 of the body is very different. The eyes (only doubtfully n gardtd 

 as appendages) may be entirely sessile, or may be elevated ujxin 

 short, subcyHndrical, more or less movable eye-stalks. The an- 

 tennulae have an articulated base, with one or two terminal, articu- 

 lated branches (flagella). The antennae have an articulated basal 

 part, with one terminal, articulated flagellum, and often the Ixisal 

 part has a lateral scalelike process: the antennal scale t)r scapho- 

 cerite. 



The mandible consists of a more or less solid part, to which an 

 articulated palpus may be attached. The maxillae are of various 

 shapes, and are probably to be regarded as mcxlifietl antcri-r 

 thoracic appendages. They consist of an inner and an nuirr 

 branch (endopodite and exopodite), which, however, are often 

 augmented by certain parts belonging originall)- to the gill ap|>a- 

 ratus. 



The most marked difference is between the thoracic and the ab- 

 dominal appendages. The fonner consist originally of a larger, 

 seven-jointed inner branch (endopodite), and a smaller, articu- 

 lated outer branch (exopodite), but the latter may be absent. 

 The seven joints of the endopodite are rather constant. allhouKh 

 some of them may become united, or others may be sulxlividetl. 

 They have received separate names, which are, from the proximal 

 to the distal end: coxa, basis, ischium, mems. caq^us. proixxlu*. 

 dactylus (or coxopodite, basipodite. etc.). In certam thoracic 

 limbs, the last two joints (propodus and dactylus) assume ■ '- m- 

 liar position, forming a chela (j^inchers, claws). 



