6 



The posterior maxillae are rather small and simple in structure, somewhat 

 resembling those in the Isopoda. As in the latter, they carry at the end out- 

 side, 2 small movable lamellae, which partly overlap each other, and are clothed 

 with incurved spines. These lamellae, which have often been described as the 

 palp, may more properly represent the modified masticatory lobe, as suggested 

 by Dr. Boas. In the genus Campylaspis, however, these lamellae are wholly 

 wanting. 



Behind these true oral parts there are 3 pairs of limbs, which, judging 

 both from arrangement and function, appear to be subservient to mastication, 

 and which accordingly ought to be termed maxillipeds. In this respect the 

 Cumacea differ very materially from the Edriophthalmia, in which never more 

 than one pair of maxillipeds are found. In the higher Crustacea (Decapoda), 

 on the other hand, the number of maxillipeds is normally the same as in the 

 Cumacea. 



The 1st pair of these maxillipeds is rather short and stout, exhibiting 

 inside the end of the basal joint a short conical lobe, clothed with peculiarly 

 modified spines and bristles. To the base of these limbs the remarkable branchial 

 apparatus is movably appended, so as to admit of being swung freely within the 

 roomy branchial cavities. As shown elsewhere by the present author, this ap- 

 paratus is composed of the modified epipodite and exopodite, the former occupy- 

 ing the greater part of the apparatus, and carrying inside it the true gill-elements 

 in the form of densely crowded lamellae, or more scattered digitiform sacs. The 

 exopodal portions of the apparatus extend straight forwards, and together form 

 a funnel-shaped tube, through which the water introduced into the branchial cavities 

 is at certain intervals expelled by the oscillatory movements of the epipodal 

 portions. They are to some extent connected with the latter at the base, and their 

 extremities are closely applied to each other, admitting of being exserted from the tip 

 of the pseudorostral projection. In some cases, they terminate in 2 incrusted 

 lamellae, which work as a valve by alternately opening and closing the anterior 

 aperture leading to the branchial cavities. In other cases, they form together a 

 long delicate tube, which admits of being protruded and again withdrawn, and 

 which is opened and closed at the tip by its own elasticity. The explanation 

 here given has been contested by some recent authors ; but after renewed 

 careful examination, I must still insist on its correctness. Anything analogous 

 to this singular apparatus is only found in the Schizopoda (Lophogastridae and 

 Mysidae) and in [the cheliferous Isopoda; but in these it is only the epipodite 

 which is peculiarly modified for branchial purposes, and in no case does this 

 part carry true gill-elements, as in the Cumacea, 



