146 



THE CRUSTACEA 



according to Hansen, a pre-coxal segment (pleuropodite of Coutiere) 

 which is distinct only in the Leptostraca and Stomatopoda. The 

 axis of the limb is continued by the endopodite which forms an 

 ambulatory leg, while the flagelliform exopodite is used for 

 swimming. There are five segments in the endopodite, termed 

 by Milne - Edwards respectively the ischiopodite, meropodite, 

 carpopodite, propodite, and dactylopodite (often abbreviated to 

 ischium, merus, carpus, propodus, and dactylus). Hansen con- 

 siders that the terminal claw which is sometimes distinct from the 

 dactylopodite represents an additional segment, making, with the 

 pre-coxa, nine segments in the axis of the limb instead of the 



prop. 



dact.--- 



FIG. 80. 

 Diagram of a Malacostracan thoracic 



seven usually recognised. It seems 

 probable, however, that this claw 

 (termed stylopodite by Coutiere) is 

 simply an enlarged spine and not 

 one of the segments of the limb. 



At the bases of the thoracic 

 limbs on the outer side are a series 

 of epipodial appendages (exites) 

 probably originally branchial in 

 function. It is not quite clear how 

 many of these appendages must be 

 attributed to each thoracic limb of 

 the primitive type, but probably at 

 least two are to be recognised, an 



WOclite attached to the COXOpodite 



appendage. 6s, basipodite ; carp, carpo- and a moepwodlte to the pre-COXal 



podite; car, coxopodite; dact, dactylopodite; ^.f 



en, endopodite ; ep, epipodites ; ex, exopo- Segment. 1 ne OOStegitCS, Or brOOu- 



^Z$ffiSS?iSg itt ' i Plates, attached to the inner side of 



the coxopodite in the female sex in 



some of the orders, and forming a pouch for the protection of the 

 eggs and young, may possibly be derived from some of these epi- 

 podial structures, as Glaus suggests. The terminology applied to the 

 thoracic limbs in systematic works differs greatly in the various orders 

 of Malacostraca. From one to three of the anterior pairs may be 

 called maxillipeds, the second and third pairs are in some cases known 

 as gnathopods, and the last five pairs are often termed peraeopods. \ 



The abdominal appendages are all biramous and are used in 

 swimming, but the sixth pair differ in form and function from the 

 others. The first five pairs are known as pleopods. They have the 

 protopodite composed of two segments (occasionally there are 

 traces of a third), and the rami are fringed with long setae and 

 assist the thoracic exopodites in the ordinary swimming move- 

 ments of the animal. The appendages of each pair are coupled 

 together by a group of hooked spines (retinacula) either on the 

 inner edge of the protopodite or on a special process of the 



