1 68 THE OCEAN WORLD. 



Cassiopea and Ccphea are two other genera belonging to the 

 same group. In Cassiopea andromeda (Fig. 57), the disc is hemi- 

 spherical, but much depressed, without marginal tentacles or peduncle, 

 but with a central disc, with four to eight half-moon-shaped orifices 

 at the side, and throwing off eight to ten branching arms, fringed 

 with retractile sucking discs. Cephea cydophora, Peron (Fig. 58), is 

 another very remarkable form of these strangely-constituted organisms. 



Having presented to the reader these few characteristic types 

 of Medusidae, we proceed to offer some general remarks upon the 

 organisation and functions of these strange creatures. We have, in 

 short, selected these types because they have been special objects of 

 anatomical and physiological study to some of our best naturalists. 



The Medusae have no other means of breathing but through the 

 skin. We remark all over the body of these creatures certain 

 prolongations of the tegumentary system, disposed perhaps so as to 

 favour the exercise of the breathing function. Certain marginal 

 fringes of extended surface, as well as the tentacles, may be the 

 special seats of this function. The organs of digestion also present 

 arrangements peculiar to themselves ; the mouth is placed on the 

 lower part of the body, and is pierced at the extremity of a trumpet- 

 like tube, hanging sometimes like the tongue of a bell. The walls 

 of the stomach, again, are furnished with a multitude of appendages, 

 which have their origin in the cavity of the organ, and which are 

 very elastic. The stomach, furnished with vibratile cilia, appears to 

 secrete a juice whose function is to decompose the food and render 

 indigestible. 



A very distinct circulation exists in the Medusae. The periphery 

 part of the stomach suffers the nourishing liquid which has been elabo- 

 rated in the digestive cavity to pass ; this fluid then circulates through 

 numerous canals, the existence of which have been clearly traced. 



It is also a singular fact, that organs of sense seem to have been 

 discovered in these Medusae, which early observers believed to Ix 

 altogether destitute of organisation. " During my sojourn on the 

 banks of the Red Sea," says Ehrenberg, in his Memoir on the Medusa 

 aurita, "although I had many times examined the brownish bodies 

 upon the edge of the disc of the Medusae, it is only in the past 

 month that I have recognised their true nature and function. Each 

 of these bodies consists of a little yellow tubercle, oval or cylindrical, 

 fixed upon a thin peduncle. The peduncle is attached to a vesicle, 

 in which the microscope reveals a glandular body, yellow when the 

 light traverses it, but white when the light is only reflected on it. 

 From this body issue two branches, which proceed towards the 



