9(5 THE VOYAGE OF H.M.S. CHALLENGER. 



distal end ; the thicker proximal end is cut out concavely, and inserted at the lower part of 

 the corner, swelling above the umbrella margin in such a manner that a small axial 

 cavity, or pedal funnel (" infundibulum pedale," fig. 3, it), remains between the two. 



The four tentacles are strong, cylindrical, hollow filaments, 4 mm. thick, thickened 

 like a club at the basis (to 6 mm.), and longer than the height of the umbrella (probably 

 several times as long in the uninjured animal). In the longitudinal and transverse 

 sections, their thick wall shows the same peculiar and complicated structure, fully 

 described by Claus in Charybdea marsupialis. 



The four perradial sense clubs or marginal bodies (" rhopalia ") lie above the umbrella 

 margin, in the ectodermal sense niches (" crypta rhopalaria or ocularia") already men- 

 tioned. The structure of these highly-developed organs of sense in Charybdea murrayana 

 is the same as in the Mediterranean Charybdea marsupialis, where they were first inves- 

 tigated by Gegenbaur in 1836, and recently and minutely by Claus in 1878. They have 

 a very complex structure, and essentially resemble those of the Peromedusae and Discome- 

 dusse, as they contain both optical and acoustic organs ; their finer structure, however, 

 varies in several respects, and in some ways very peculiar. Each sense club is fastened 

 by a thin peduncle into the sense niche of the exumbrella, and is partly covered 

 externally by the protective scale, which projects like a roof over the exodermal aperture 

 of the rhopalar niche. It contains a large otolite sac containing numerous crystalline 

 endodermal otolites in its club-shaped swollen terminal part. The six eyes, two larger 

 unpaired in the perradial middle line, and four smaller paired on the two sides of the 

 unpaired, lie above the otolite sac ; each unpaired eye consists of a pigment cup, a thick 

 lens, and a powerful corpus vitreum lying between them ; the lens is wanting in the 

 smaller paired eyes. A very large ganglion opticum of a highly developed structure 

 forms the nerve centre of the optical apparatus. 



The nervous system has the same high centralisation as in the other CubornedusEe, and 

 corresponding to their highly developed organs of sense, it shows itself in a more com- 

 plete and more centralised form, than in the other Acraspeda ; in this respect it attains 

 the highest stage of formation among all Acraspeda. The central nervous system, which 

 was discovered in Tamoya by Fritz Muller (1859), consists of a complete nerve ring and 

 of eight ganglia, the four larger perradial being placed at the basis of the sense clubs, 

 and the four interradial at the basis of the tentacle pedalia ; from the perradial ganglia 

 sense nerves go out to the organs of sense and motor nerves to the longitudinal muscles, 

 while motor nerves go out to the tentacles from the interradial ganglia. The former 

 always lie considerably higher than the latter, so that the nerve ring rises in a vaulted 

 arch from the rhopalar niche to the basis of the pedalia. The whole nerve ring (figs. 2-8, 

 re) therefore forms four depressed arches. Their highest part lies perradially, their 

 lowest part interradially. The nerve ring Hes embedded in a groove of the subumbrella, 

 interrupting its muscular plate, and consists of a clear axial cord and two more turbid 



