CRUSTACEA OUTER ORGANISATION 



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the maxillipede, on which an epipodial appendage in the shape of a firm plate has 

 been retained (Fig. 217, F). The Anisopoda deviate in many ways from other Isopoda 

 (Fig. 217, B-D], especially the genus Apseudes. The anterior thoracic foot (maxilli- 

 pede) () possesses a large epipodial appendage, which by its vibration causes a 

 constant current of water in the respiratory cavity formed by the shell-fold. On 

 the 2d and 3d thoracic feet (0, D) of Apseudes there are rudimentary exopodites, 

 a fact of great importance in tracing back the thoracic feet of the Arthrostraca to 

 biramose feet. The thoracic feet of the second pair are transformed into strong 

 chelate feet in the ordinary manner, i.e. the ultimate (5th) joint of the endopodite 

 is opposable to a distal process of the penultimate (the 4th). 



FIG. 219. Thoracic feet of Diastylis stygia ? (after G. O. Sars). A, 1st, B, 2d, C, 4th, D, 

 6th thoracic feet, ep, Epipodial plate ; &r, gill on the same ; en, endopodite ; ex, exopodite, which 

 in A is a hard lamella ; Irp, brood plate. 



Thoracostraca. In the Cumacea (Figs. 199 and 219) the most anterior thoracic 

 foot has become a maxillipede. The remaining thoracic feet are long. Brood- 

 lamellae occur on the basal joints of the 2d to the 6th pairs in the female. The 

 exopodite is wanting in the 1st (?), 2d, and 8th pairs ; in the female usually also in 

 the 6th and 7th ; on the other feet it is present and serves for swimming. The 

 endopodite has 5 joints. An epipodial appendage is developed only on the 1st 

 thoracic foot (maxillipede), but here is very large. It has numerous branchial tubes. 

 The distal joint of the protopodite of the maxillipede carries a masticatory ridge. 



Among the Stomatopoda (Figs. 200 and 220) the 5 anterior pairs of thoracic feet 

 are formed very differently from the 3 posterior pairs. The latter arise from the 

 3 free posterior segments of the thorax, which are not covered by the cephalo- 



