30 ZOOLOGY. 
The light is usually produced under exciting circumstances, or when the 
animal i is disturbed, and all parts do not produce light. Spallanzani found 
that in Cutting off the margin for about half an bra the latter remained 
phosphorescent, which was not the case with the disk. ; 
Orver 2. Purmonierapa. The following species of this order are figured ; 
Thaumantias cymbaloidea (pl. 76, fig. 73), Northern Seas. Aurelia aurita, 
Linn. (jig. 74), Northern Seas; six to ten or eleven inches in diameter. 
In this genus the mouth is surrounded with four arms, and the central 
peduncle is wanting. This species has a bluish disk, fringed with 
slender tentacles, and having eight marginal ocelli, which are black, with a 
red point above. Beneath ete are a long fiacell central arms, with 
the mouth between them. Sometimes the margin of the arms contains eggs. 
The ovaries, however, have their openings between the base of each pair 
of arms ; hee are nk of them shaped like a horse-shoe, and of a purple 
color, which renders them visible from above, as seen in the figure. 
Orper 3.  Criograpa. This order (also named Ctenophora by 
Eschscholtz) is named from its organs of motion, which consist of a series 
of flat phosphorescent vibrille, arranged longitudinally upon the surface of 
the body, along the eight ribs, and by the action of which progression is 
effected. These vibrille are arranged with their flat surfaces nearly in 
contact, and they are raised slowly and struck rapidly. Some authors 
suppose them to subserve the purpose of gills as well as organs of locomotion. — 
The genus Beroe, which is a good example, varies in form from globular to 
cylindrical, but a little compressed. The cavity beneath is very large, and 
the animal moves with the mouth foremost. In addition to the mouth there 
is an excretory orifice. Cestwm veneris has a ribbon-shaped body, the two 
margins of which are fringed with beautifully colored phosphorescent 
vibrillee, which at night give the animal the appearance of a band of flame, 
as it moves through the water. It attains the length of three or four 
feet. 
Orver 4. CrrricrapA. The form is discoidal, and there is an internal 
subcartilaginous discoidal skeleton, which distinguishes them from the 
Pulmonigrada. In Porpita (pl. 76, fig. 83) the margin is fringed with 
stout claviform tentacles, provided with three ranges of pedunculated 
glands or suckers. The stomachal pedicle is large, and surrounded by 
numerous tentaculiform cirri, by means of which locomotion is effected. 
These bear some resemblance to the tentacles of the Actinize, to which 
Blainville thinks the order has some affinities. In Velella (V. sporans, 
Forsk., pl. 76, jig. 84), besides an oval cartilaginous skeleton, there is a 
vertical process arising from it which supports a crest-like membrane. 
Orper 5. Puysocrapa. This order was called Hydrostatic Acalephz by 
Cuvier, a designation which, like the proper name, points to a peculiarity 
of structure, namely, the support of the body by one or more air-vessels, 
which cause the animal to float. Physalia physalis, Linn. (pl. 77, fig. 1), 
possesses stinging qualities ; it inhabits the Gulf of Mexico and the Atlante, 
and is known to sailors as the Portuguese man-of-war. The air-vessel is 
very large, and has a small aperture at each end, from which the air can be 
234 
