(g) _Nerve Ring._ It is in the possession of a clearly defined nerve ring that the Cubomedusæ differ from all other Scyphomedusæ whose nervous system has been carefully studied. The nerve ring shows very plainly on the surface of the subumbrella as a well-defined clear streak. Its course is zig-zag or festoon-like. In the interradii, at the basis of the tentacles, it lies not far from the bell margin. In the perradii it rises to the level of the sensory clubs. This very striking arrangement is understood at once when it is remembered that the sensory clubs represent the four perradial primary tentacles, and were originally situated on the margin. When all the rest of the margin grew down and away from the four sensory clubs, fusing below them to form the present intact edge of the bell, the four portions of the nerve ring that lay in the perradii were left at the level of the sensory clubs, and the originally straight nerve ring was thus bent into a bow in each quadrant. The finer structure of the nerve will be treated of in the special part to be devoted to the nervous system. c. _Internal Anatomy._ 6. _Stomach._ The shape of the stomach is approximately that of a biconvex lens, as seen in Fig. 4, which represents a Charybdea cut in halves longitudinally in the perradius. The lumen of the proboscis (the buccal stomach according to Haeckel’s terminology) communicates directly by a funnel-shaped enlargement with the stomach proper, or central stomach of Haeckel. The term basal stomach is carried over by Haeckel from the Stauromedusæ, where it has considerable significance, to the Cubomedusæ, and applied to the upper part of the central stomach. In the stalkless Cubomedusæ, however, it has no significance so far as actual structure goes, and our knowledge of the development of the Cubomedusæ is as yet too simple for us to say that the upper part of the main stomach represents what remains of the basal stomach of an earlier pedunculated stage.