AMPHIPODA. 495 



the Gammarina and some Hyperina often expanded into wide 

 lamellae* (Fig. 304) which may be suturally or movably united 

 with the thorax. In some genera they are much reduced and in 

 Phronima and its allies they do not exist as separate segments. 

 The ends of some of the anterior limbs are frequently modified 

 for prehension. In a few cases (Hyperina) a true chela is pro- 

 duced, the terminal or two terminal segments being opposable 

 to a projecting process on the preceding segment (Figs. 307) ; 

 but more usually the limb ends in a clasping "hand" in which 

 the terminal segment folds back, like the blade of a pocket 

 knife, on it spredecessor. In either case the structure is often 

 larger in the male. In the Caprellidae (Fig. 308) the number of 

 legs is often reduced. 



It is probable (as already stated, p. 439) that both the bran- 

 chiae and oostegites are to be regarded as epipodial appendages 

 of the thoracic limbs, and homologous with the two epipodia 

 of the legs of Anaspides. 



The branchiae are usually simple lobes attached near the bases 

 of six or fewer of the posterior thoracic legs, and project on the 

 inner sides of the limbs. They may be attached to the coxopodite 

 of the limb or to the adjoining ventral surface of the segment 

 of the body. On the view of their epipodial nature we should 

 expect to find them attached to the outer surface of the limb, 

 and in some forms at any rate (Gammarus) the branchial pedicle 

 springs from the outer side of the posterior margin of the leg, 

 although the plate curls round and lies internal to it. In some 

 Lysianassina the structure of the branchiae is complicated by 

 the development of secondary folds on one or both faces. In the 

 Caprellidae, though some segments of the thorax are without 

 limbs, the branchiae are nevertheless present on them. 



The oostegites usually spring from the coxopodites, nearer the 

 base than the branchiae, or from the adjoining surface of the 

 thoracic segment, and curving inwards overlap one another 

 across the middle line, forming the floor of the brood pouch. 

 They are borne by from two to four pairs of legs, namely those 

 belonging to the 4th and 5th, or to the 3rd to the 6th thoracic 



* These coxopodites are often termed " epimerites " in works on 

 amphipod anatomy, but as this word is used by some authors for the 

 region of the body between the base of an appendage and the pleuron, 

 and by others for the pleuron itself, it is clearly inconvenient to apply 

 it to a part of the appendage. 



