652 ACALEPHA. 



bably ovaries. Notwithstanding its very singular shape, this animal may be considered as resembling 

 a Callianira, in which the wings are excessively developed. 



There is but one known species, C. Veneris, " the Girdle of Venus," which, considered as a ribbon, is five feet 

 long-, and two inches broad ; but as an animal, it is five feet broad, and two inches high. It inhabits the Medi- 

 terranean ; but its substance is so tender, that it is difficult to preserve an entire specimen. 



The two genera following, though long included among the Medusae, ought rather to form a small separate family 

 of the order, on account of the interior cartilage which supports the gelatinous substance of their body. 



Porpita, have a circular cartilage, and the surface marked with concentric stria?, crossed by radiating ones. 

 The upper surface is simply invested with a thin membrane, which projects beyond it; but the under surface is 

 furnished with many tentacula, the external ones long, and beset with small cilia terminating in little globes; 

 these sometimes contain air; and those toward the middle are the shortest, simplest, and most fleshy. In the 

 middle of these tentacula the mouth is situated, in the form of a small projectile proboscis. It leads to a simple 

 stonjach, surrounded by a coat of glandular substance. There is only one known species, which is of a black 

 colour, and found in the Mediterranean and the warmer seas. 



Velella, have the mouth and tentacula like the preceding, only the latter are not ciliated. The cartilage is oval, 

 and has a crest of some elevation passing obliquely across it, and it is transparent, without striae. There is but one 

 known species, which inhabits the same seas as Porpita. It is fried and eaten. 



THE SECOND ORDER OF THE ACALEPHA. 



THE HYDROSTATICA. 



The members of this order are distinguished by one or more vessels filled with air, by means 

 of which they keep themselves suspended in the water. Appendages, exceedingly membranous, 

 and varied in their forms, some of them probably suckers, and others ovaries, are attached to 

 the air vessels, and with these constitute the whole visible organization of the animal. 



Physalia, — 



Consists of a large oblong air vessel, with an oblique and wrinkled salient crest on the upper surface, and 

 furnished below, near one of the ends, with a number of cylindrical appendages, which have their 

 extremities of different forms, but they all communicate with the air vessel. The middle ones are 

 beset with groups of little filaments ; and the lateral ones end in two threads each, one of which is 

 usually very long. There is apparently a very small opening at one end of the air vessel ; but there 

 are no intestines visible, though there is an inner vessel, with a thinner tunic, from which cosca 

 proceed to the processes of the crest ; and no nervous, or circulating, or glandular system is visible. 

 They float upon the surface of the sea when smooth, and the crest answers the purpose of a sail. 

 When living, it has two filaments much larger than the others, which are gemmed with a sort of pearly- 

 looking drops. When touched it stings or burns the fingers, like those Medusae which are called " sea 

 nettles." They are found in all the warm seas, and have been, strangely enough, confounded with 



Ilolothuria. 



Phvssophora, — 



Resemble Physalia in their general characters ; but the air vessel is much smaller, has no crest, and is 



often accompanied by lateral ones still smaller. The tentacula, which are very numerous, are suspended 



in a bunch under the air vessels. 



The Phi/ssop'iora, properly so called, have the secondary air vessels placed laterally under the principal one; 

 and the tentacula are conical, cylindrical, or terminating in thread-like appendages, the last being susceptible of 

 considerable elongation. 



Hippopus, have only lateral vesicles, semicircular, or resembling the foot of a Horse. These are arranged in 

 two rows like the grains on the spikes of certain grasses ; and by their united contraction and dilatation, the 

 animal can move with considerable velocity. [As the Physalia have been compared to little sailing boats, so these 

 may be looked upon as a sort of steamer in miniature.] Capulitcv, have vesicles attached in two regular rows, 

 often of a pretty long axis. Racemida, have the vessels small and globular, and united into an oval mass. 

 Rhizophyza, have a single air vessel on the top of a stem, on the sides of which the tentacula are attached. 

 Stephanomia, have the secondary air vessels blended with the tentacula around the stem. 



DiPHYES, 



Are curious animals, different from the Hydrostatic Acalepha, and yet, perhaps, resembling them more 

 than any other animals in the system. Two of them are always found together, one within tlie cavity 



