B54 DIVISION IV. RADIATA.—CLASS III. ACALEPHA. 
are bristled with points or filaments, connected with a kind of vessel. They 
receive their nourishment through a large and capacious mouth. The num- 
ber four plays the same important part in the umbrella and globe-shaped 
Acalephe, as the number five in the construction of the star-fishes. All 
parts of the body are divisible by four, and radiate from a centre. 
ORDER II. THE HYDROSTATICA. 
The members of this order, according to Cuvier, are distinguished by one 
or more vessels filled with air, by means of which they keep themselves sus- 
pended in the water. Appendages exceedingly membranous and varied in 
their forms are attached to the air-vessels, and with these constitute the 
whole visible organization of the animal. The order comprises the genera 
Physalia, Physsophora, and Diphyes. 
PuysaLia.— The Physalie have a large oblong body, —a mere air- 
vessel, — with an oblique and wrinkled salient crest on the upper surface. 
They swim or float upon the sea when smooth, the crest answering the pur- 
pose of a sail. The tentacles can be rolled together, or rapidly extended to 
a length of twenty feet. They employ them as a net, and, dragging them 
through the water, entrap small fishes, which are paralyzed by the venomous 
secretion of their funnel-shaped suckers, and conveyed to the numerous 
mouths of the compound animal, which, sucking like leeches, pump out 
their nutritious juices. 
Puyssornora.—The members of this genus have no crest, the air- 
vessel is much smaller than in the preceding, and the numerous tentacula 
are suspended in a bunch under the air-vessel. 
Sars, and other naturalists, consider these animals to be merely alternating 
generations of the bell-shaped Acalephx, belonging undoubtedly to the most 
curious denizens of the ocean. They are composite creatures, forming a 
kind of social republic, in which some individuals are exclusively destined 
for locomotion, while others provide the colony with food, or are charged 
with the propagation of the species. A whole republic grows out of a larva 
or egg of a bell-shaped medusa, which, like a budding plant, gradually 
unfolds itself to this closely-united confraternity, and the latter in its turn 
gives birth to simple bell-shaped jelly-fishes. It has ‘also been discovered 
that the delicate feathery forms of the sea-wreaths, sea-feathers, and sea- 
bells, — sertulariev, plumularie, and campanularie, — which were for- 
merly supposed to be polypes, proceed from medusa larve, and in their turn 
bring forth perfect Acalephe. 
Dirnyes.— The members of this genus are remarkable specimens of 
