28 ZOOLOGY. 
two feet, and the weight of large ones reaches fifty or sixty pounds. Yet- 
this great mass is composed almost entirely of water, which pervades the 
tissues, and these are of such extreme tenuity that the weight of one of 
these masses is reduced by desiccation to grains instead of pounds. 
The more familiar forms belong to the Pulmonigrada, also termed Disco- 
phora, which may be compared to an expanded umbrella, or toa mushroom, 
the alternate contraction and expansion of which enable the body to move 
through the water with the convex or upper surface foremost; a mode of 
progression which has afforded a name to the order, from its resemblance 
to the action of lungs. | 
The beauty of many of these animals equals anything in organic nature ; 
the colors are prismatic or entirely wanting, and in the latter case, the - 
gelatinous transparent body resembles a mass of colorless liquid gum, which 
can only be distinguished by its motions from the water which surrounds it. 
‘‘ When in a jar or basin they are often very difficult to distinguish, but 
by placing the vessel in the sun, we see their shadows floating over the sides 
and bottom like the shadows of flitting clouds on a landscape. These soon 
guide us to the creatures themselves, and before long we distinguish their 
ocelli and colored reproductive organs.”—Forbes. 
The disk forming the greater part of the body varies from hemispherical 
to flattened discoidal, and is sometimes lengthened into a conical or sub- 
cylindrical form. The central portion is thickest, and the inferior surface 
is concave. The margin is either entire or fringed with tentacles, which 
vary greatly in length, number, and form. Some of these tentacles have a 
colored spot at their base called an ocellus, and upon this Forbes has divided 
the Discophora into two groups; namely, the Steganophthalmata (covered 
eyes), in which the ocelli are protected by membranous lobes, and the 
Gymnophthalmata (naked eyes), in which the ocelli are not protected. -The 
former are more highly organized than the latter, and in most of the genera 
the sexes are not united in the same individual. Agassiz has discovered a 
nervous ring around the mouth, with branches extending to the ocelli; an 
arrangement which resembles that in the Echinodermata. Ehrenberg had 
made a less distinct announcement, and Dr. Grant announced the discovery 
of a nervous system in Beroe, in the year 1833. 
From the centre of the concavity of the disk arises the peduncle, which 
varies much in size and shape, in some genera forming a considerable 
portion of the animal, and in others being reduced to a slender extensile and 
contractile tube, at the extremity of which the mouth is situated. The 
cavity of the peduncle, or its base, is the stomach, whence branches are sent 
towards the disk, around the margin of which there is a canal connecting 
with them. These radiating gastro-vascular branches vary in number 
from four to twelve or more. In the naked-eyed genera they are seldom 
branched; and when they are, the branches run to the marginal canal, as 
in the genus Wilsia* (Forbes, Monog. of the British Naked-eyed Meduse 
* Named after Dr. Will, who wrote on this subject. 
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