LUMINOUS ORGANS 259 
Cumacea and some of the Isopoda. The second maxill 
exhibit 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 maxillz 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 Lophogaster, is of very 
considerable size, almost 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 branchiz 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 Lopho- 
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