648 MEDUSA OF THE WORLD. 



C. fronJosa can at once be distinguished from C. xamackana by its amber color, the 

 absence of ocelli on its rhopalia, the absence of a sucker-like concavity upon its exumbrella, 

 and by the^fact that it has constantly 12 marginal sense-organs, whereas C. xamachana has 

 II to 23 (see plate 69). It is far less hardy in aquaria than C. xamachana. 



According to Bigelow, 1893, in the adult female the mouths disappear from the oral 

 disk while at the same time the oral vesicles increase in number until they are closely crowded 

 together and completely cover it. The eggs are discharged from the ovaries into the stomach, 

 where cleavage begins; they then pass out on to the oral disk and are to be found there in large 

 numbers, cemented together in small, reticulated clusters at the bases of the vesicles; they 

 remain there until some time after they have become ciliated planulae. Bigelow reared the 

 scyphostomae of this species to the 8-tentacle stage. The young scyphostoma appears to be 

 entirely similar to those of other species of Cassiopea. 



Dr. R. P. Bigelow has shown that while the vesicles on the oral surface of the disk serve 

 to protect the young, those of the mouth-arms serve to capture food. These vesicles usually 

 stand upright, but upon being struck by an unwary copepod they bend down and close the 

 mouth of the nearest funnel in the manner of a lid. The prey thus finds itself within one of 

 the mouths, tightly shut in by the overlying vesicle. 



Cassiopea ornata Haeckel. 



Cassiopea ornata, HAECKEL, 1880, Syst. der Medusen, p. 570, taf. 37, fign. 1-8. HAMANN, 1881, Jena. Zeit.fiir Naturw.,Bd. 15, 

 p. 248 (structure of the mouth-arms). 



Bell 100 to 120 mm. wide, 30 to 40 mm. high, flat and shield-shaped. 16 rhopalia, 80 

 lappets, 96 white spots, as in C. andromeda. Mouth-arms cylindrical, slender, and somewhat 

 longer than bell-radius, not broad and flat as in the typical C. andromeda. There are only 

 small, club-shaped vesicles between the mouths. The characteristic feature of this species is 

 said to be the presence of 2 distinct ring-canals. The inner ring-canal connects the 16 principal 

 radial-canals at an annulus some distance inward from the margin, while the outer ring- 

 canal is at the margin. The 16 inter-rhopalar radial-canals are narrower than the rhopalar, 

 and soon lose themselves in the network of anastomosing vessels of the subumbrella, whereas 

 the 16 rhopalar canals extend straight out to the sense-organs. The network of vessels becomes 

 fine-meshed on the inner side of the ring-canal, but on its outer side it gives off a wide-meshed 

 network, the meshes of which become finer as they near the bell-margin, where there is a 

 marginal ring-canal. These hypothetical ring-canals are so peculiar and unlike the simple net- 

 work seen in other species of Cassiopea that the fact of their existence requires confirmation. 

 Haeckel alone has observed them. The medusa is from the Pelew Islands and New Guinea. 



I find among the collections of the U. S. Fisheries Bureau steamer Albatross seven speci- 

 mens of a medusa which appears to be a closely related variety of, if not identical with, C. 

 ornata. None of these has the remarkable ring-canals figured by Haeckel, and this leads me 

 to doubt their existence in Haeckel's medusa. The dimensions in mm. of the largest of these 

 medusae are as follows: Bell 76 wide; exumbrella flat, smooth and without an aboral sucker- 

 cavity; arm-disk 39 wide; mouth-arms 31 long, stout and flattened laterally, with 9 to 12 short, 

 stout, blunt, dentritically arranged side branches. A few very small, flat, club-like appendages 

 less than I mm. long scattered among the mouths of the mouth-arms; but these become larger 

 near the arm-disk. The arm-disk itself is thickly covered with irregularly shaped tuber-like, or 

 truffle-shaped, appendages, the largest being 3 to 4 mm. long. There are 16 rhopalia. 5X16 

 blunt, square-edged, marginal lappets. 32 tree-like radial-canals which give off an anasto- 

 mosing network, but no distinctly differentiated ring-canal. These medusae were obtained in 

 the following localities in the Philippine Islands in 1908: 3 large specimens from near 

 shore at Tataan, Simaluc Islands, February 19 and 20; 3 from Subic Bay, January 7, in a 

 seine, and I from Catbalogan, Samar, on April 16. 



Cassiopea ornata var. digitata Maas. 

 Cassiopea ornata var. digitata, MAAS, 1093, Scyphomedusen der Siboga Expedition, Monog. 11, pp. 40, 45, taf. 4, fign. 26, 30. 



Bell about 100 mm. wide, very flat, without an aboral concavity or a dome. 16 marginal 

 sense-organs, 32 rhopalar and 3X i6,or more, velar lappets which are, however, quite irregularly 



