LUMINOUS OEGANS 259 



Cumacea and some of tlie Isopoda. The second maxillge 

 exMbit exteriorly at the base a very conspicuous mam- 

 milliform prominence, which Sars supposes to be a 

 phosphorescent organ. Dr. v. Willemoes Suhm considered 

 it an accessory eye, and hence gave the genus a name 

 meaning ' light in the jaw,' which is equally appropriate 

 to the new explanation of this curious prominence. The 

 lamellar exopods of these maxillse fit pretty closely into 

 the lateral emargination of the carapace at each side of 

 the buccal area, ' forming, as it were, a kind of piston, by 

 the oscillatory movements of which the postero-anterior 

 current of water produced beneath the free portion of the 

 carapace may be regulated.' The first maxillipeds have 

 the basal part much widened, the indistinctly separated 

 second joint in some species carrying a rudimentary 

 exopod, but not in others ; the basal joint has an epipod, 

 a freely movable membranous plate, projecting within the 

 branchial cavity. This, ' as in Lopkogaster, is of very 

 considerable size, alm.ost equalling in length the whole 

 maxilliped, and exhibits a narrow lanceolate form, the 

 apex being somewhat recurved. Its function, too, is more 

 properly to produce, by its rhythmical movements to and 

 fro, the current of water flowing beneath the free portion of 

 the carapace, and bathing the gill-branches attached out- 

 side the bases of the legs.' The seven following pairs of 

 appendages have the fifth joint elongate, the exopod de- 

 veloped into a powerful swimming branch, of which the 

 base is muscular and the terminal part multiarticulate and 

 setiferous. The complex branchiae are strongly developed 

 at the bases of all the pairs, except the last, on which 

 they are small and rudimentary. The pleopods in both 

 sexes are developed in the same manner as powerful 

 swimming organs. The sixth segment of the pleon has a 

 transverse suture, as in Lophogaster. The telson is large, 

 channelled along the middle, and after tapering to the 

 apex there ends in an almost semilunar projection. Of 

 this strange genus nine species are now known, ranging 

 in depth from 255 to 2,200 fathoms, and over almost all 

 the ocean. The first species described was called Lo^lio- 

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