OF THE ACALEPH/E OF NORTH AMERICA. 307 



limited space of the central portion of the disk, were to extend, as a long, radiating arm, 

 from the centre to the periphery, and that its margins were not elongated, but consisted 

 merely of narrow ribbon-like membranes laid flat against each other, and following the 

 fissure of the mouth with uniform width for its whole extent, and that its membranes 

 were more or less lobed along their whole margin, and we should have the mouth of 

 Staurophora. 



Indeed, in our Medusa this cross consists of a narrow fissure in the centre (Plate 

 VII. Fig. 15 and 12), towards which the four arms converge ; and each arm of the 

 cross, when properly examined, is found to consist of a narrow fissure, inclosed by two 

 membranes pressed against each other ; but the lower margin of each diverges some- 

 what, and is undulated and lobed for its whole length. Near the periphery, however, the 

 two membranes of each arm converge and unite (Fig. 13 and 14), and thus close the 

 fissure completely, and turn it into a narrow tube, which extends further and com- 

 municates freely with the circular tube extending along the base of the tentacles. Upon 

 unfolding these double membranes along each ray, it is easy to penetrate into the fissure 

 between them, and also to ascertain that this fissure is continuous, and that the fissures 

 of the four arms of the cross meet in the centre in an oblong open space surrounded by 

 folds inclosing the four fissures, which meet here in continuous lobes, and thus form a 

 free entrance to the central cavity, which extends into the arms. * 



There can be, therefore, no mistake about the real nature of this open space, and the 

 fissures with which it communicates. The central opening (Fig. 12, a) is the mouth ; 

 the four fissures of the four arms of the cross are its extensively prolonged angles ; and 

 the fringes which encircle them are the ribbon-like fringed margin of the mouth, and are 

 truly homologous with the mouth of all other Discophorous Medusae. So that Stauro- 

 phora, far from being destitute of mouth and stomach, is formed upon the same plan 

 with the common Discophorous Medusae, with this single difference, that the opening of 

 the mouth is very narrow and small, and somewhat oblong, and its angles very prom- 

 inent externally, and unusually developed. 



But we have direct evidence that this cross-like opening is really the mouth, and 

 that its whole extent is to be considered as the opening of the mouth, and the central 

 cavity more properly as the main cavity of the body : for I have often seen this Me- 

 dusa feeding upon other species of small size. In a glass jar, in which I kept alive for 

 weeks specimens of Staurophora with various kinds of Sarsise, Tiaropsides, and young 

 Aureliae, I have often seen the Staurophora seize upon the smallest of these animals, 

 inclose them between the folds of its central cross, and swallow them gradually, 

 completely surrounding them by its folds. Such small Medusae were seized, not only 



