JELLY-FISHES. gj^ 



The body of Aurelia, like that of Cyanea, is disk-shaped, but has a creamy-white color. 

 There arc in this genus as in the last, eight marginal sense-bodies, each covered by a 

 hood to which reference has already been made. A great difference between the two 

 genera is in the development of the appendages to the oral side of the body, and instead 

 of there being eight clusters or bundles of tentacles as in Cijanea, there is in Aurelia a 

 simple continuous circle of short filaments set around the disk-margin. The tentacles 

 are relatively much smaller than those of Cyanea. 



One of the most important characteristics of Aurelia is to be found in the structure 

 of the mouth and oral appendages. Instead of a curtain hanging down from the 

 middle of the disk, the mouth of Aurelia is formed in the following manner. From 

 the central region of the oral surface of the disk the oral appendages are suspended 

 by four gelatinous pillars. Between each pair of these pillars there is a circular 

 opening which communicates with a central cavity in which the sexual organs 

 lie. Below the sexual openings the pillars fuse, forming a gelatinous ring sun-ounding 

 the mouth and serving as a basis of attachment for certain organs, developments of the 

 lips, called the oral tentacles. These oral tentacles are four in number, and are 

 commonly carried extended radially from a central mouth-opening. Each oral 

 tentacle has no resemblance to a inarginal tentacle such as is found on the edge of 

 the disk in Cyanea or Aurelia, but is short and thick, smooth above, and bearing on 

 its under side a deep groove which, extends the whole length of the oral arm from 

 its distal tip to the central mouth. On the ridges which enclose this groove are 

 found at intervals peculiar, small, suctatorial mouths. The entrance to the stomach or 

 the large mouth in Aurelia is centrally placed on the oral side of the disk, and 

 communicates directly with a disk-shaped cavity, the stomach, which lies directly 

 above it. The lower floor of the stomach is formed by the oral surface of the bell, 

 a muscular layer, from which the four cylindrical bodies which support the oral 

 gelatinous ring are suspended. The roof of the stomach, or the gelatinous wall of the 

 bell, IS continued just above the mouth into a pyramidal jelly-like projection, which, 

 however, does not protrude outside the mouth-opening. 



The marginal sense-bodies of Aurelia are accompanied on either side by a gelatinous 

 extension or lappet which extends outward and hangs slightly downward. On the 

 aboral surface of the bell, in the neighborhood of the hood which covers the sense-body, 

 there is a raised circular area of doubtful function which is not found in the vicinity 

 of the sense-organs in Cyanea. This disk is called the simiespolster, and is, as its 

 name signifies, probably an organ of sensation. 



Of the many extraordinary genera of DiscojDhorous medusffi, one of the most 

 peculiar is the genus Cassiopea, especially a species called C. frondosa found about the 

 Florida Keys. This we may consider as the type of the family Cassiopeid^. Apart 

 from its curious habitat, being attached to the coral mud as has been mentioned above, 

 it is remarkable in the peculiar arrangement of the complicated oral appendages which, 

 although differing greatly from similar organs in the two genera already mentioned, 

 are typical of several of genera belonging to the same great grou]:!. 



Cassiopea frondosa is found lying upon its aboral surface on the mud near coral 

 islands in Florida and elsewhere in tropical seas. As one floats in a boat over these 

 curious jelly-fishes, they look very similar to an algous growth on the sea-bottom, and 

 are easily confounded with some of the forms of corallines which abound on the neigh- 

 boring sheltered submarine banks. If, however, the medusa be closely scanned, it will 

 be found to move portions of its body voluntarily, and a throbbing or vibration, espec- 



