F. S. CONANT ON THE CUBOMEDUS^. 13 



layer is shown in Fig. 39. Under the head of musculature belonging to 

 the subumbrella must be included also the radial, or longitudinal muscles 

 at the bases of the pedalia, which were mentioned before (Fig. 16, mt). 

 The mouth lobes and proboscis also are highly contractile and muscular, 

 (g) Nerve Ring. It is in the possession of a clearly denned nerve 

 ring that the CubomedusaB differ from all other Scyphomedusae 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 under- 

 stood 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 Stauromedusae, where it has considerable significance, 

 to the Cubomedusa3, and applied to the upper part of the central stomach. 

 In the stalkless Cubomedusae, however, it has no significance so far as 

 actual structure goes, and our knowledge of the development of the 

 Cubomedusas 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 peclunculated stage. 



The epithelium of the roof of the stomach is not specially differenti- 

 ated and apparently has little or no part in digestion. The epithelium of 

 the floor, on the other hand, is composed chiefly of very high and thickly 

 crowded columnar cells which are usually described as coarsely granular, 



