106 THE VOYAGE OF H.M.S. CHALLENGER. 



external side of the basal part, the eye opposite on its concave internal side, the tactile 

 plate below the eye, and the free auditory club hidden in the spacious auditory niche 

 (fig. 20, on). The olfactory depression or olfactory funnel (" infundibulum olfactorium," 

 oz) forms a flat conical depression in the convex exumbral side of the thickened basal 

 part ; its endodermal epithelium is laid in delicate folds, and consists of rod-shaped sense 

 cells (olfactory cells?). Opposite it, on the concave subumbral side, there is a broad black 

 brown pigmented pad (fig. 20, op), in whose centre the unpaired axial eye lies embedded, 

 as in Na usithoe ; this seems to contain a concave-convex lens in the middle of a darker 

 pigmented knob (oc). Below the knob a narrow dark pigmented band runs out, 

 which projects more strongly convexly, bears a variously shaped epithelium with long 

 tactile hairs, and probably represents a tactfle plate (op). The auditory club (oh) rises on 

 a thin stalk outside this plate (on its abaxial side) ; it hangs freely down in the concave 

 rhopalar niche (on), and is surrounded protectively towards the outside by the broad 

 concavo-convex protective scale or auditory scale (os) ; the blunt lower margin of the 

 latter is folded over above towards the inside. The solid auditory club, whose ectodermal 

 epithelium bears long auditory hairs, encloses a spheroidal or subspheroidal otolite 

 (fig. 20, ol ; fig. 21) in its free swollen distal end. This otolite is crystalline, and trans- 

 parent and shows many irregular, polygonal, slightly convex facets, as well as a 

 sharply projecting granulation on its upper surface. Several smaller otolites seem added 

 to the larger one at the proximal end. 



The eight tentacles (t), which alternate with the eight rhopalia, and therefore He 

 adradially, spring further above in deeper incisions of the umbrella margin. They are 

 nearly as long as the height of the umbrella, cylindrical, pointed like an awl at the 

 distal end, and swollen to a cone at the proximal basis. A short canal (a branch of the 

 eight adradial coronal pouches) runs some way into the basal part of the tentacles which 

 otherwise are solid. Their principal mass forms a soft, elastic, chordal axis, composed of 

 large vesicular endoderm cells. The ectodermal covering consists partly of thread cells, 

 partly of tactile cells, and partly of epithelial muscular cells. The long muscular fibres of 

 the latter run longitudinally and form a strong longitudinal muscle on the axial side of 

 the tentacles. 



The sixteen marginal lobes (hn) lie subradially, in the middle between the eight adra- 

 dial tentacles and the eight alternating rhopalia. They are obliquely oval, with unecpial 

 sides, as their tentacular margin is nearly twice as long as their rhopalar margin. Each 

 marginal lobe is considerably thickened in its proximal half, by the inverted bifurcate 

 branches of each two adjacent pedalia, whilst its distal half is formed by a very delicate, 

 thin-membraned, almost triangular patagium (lp>). 



The gastrovascular system (PI. XXVII. figs. 2-10; PL XXVIII. figs. 12-15) of 

 Nauphanta appears at first sight very simply formed, and not essentially different from 

 that of Ephyrula, the known common germinal form of the Discomedusse. On closer 



