168 THE OCEAN WORLD. 
Casstopea and Cephea 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 cyclophora, Péron (Fig. 58), is 
another very remarkable form of these strangely-constituted organisms. 
Having presented to the reader these few characteristic types 
of Medusidz, 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 Medusze 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 
it digestible. 
A very distinct circulation exists inthe Medusz. The peripheric 
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 Medusz, which early observers believed to be 
altogether destitute of organisation. ‘During my sojourn on the 
banks of the Red Sea,” says Ehrenberg, in his Memoir on the M/edusa 
aurita, “although I had many times examined the brownish bodies 
upon the edge of the disc of the Medusz, 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 
