30 ZOOLOGY. 



The light is usually produced under exciting circumstances, or when the 

 imiiual is disturbed, and all parts do not produce light. Spallanzani found 

 that in cutting off the margin for about half an inch, the latter remained 

 phosphorescent, which was not the case with the disk. 



Order 2. Pulmoxigrada. The following species of this order are figured ; 

 T/iiunnantias ci/mhah>idea {j>I. 16, jiff. To). Xorthern Seas. Aurelia autüta, 

 Linn. {ji^. 74), Xorthern 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 there are four long fringed central arms, with 

 the mouth between them. Sometimes the mai'gin of the arms contains eggs. 

 The ovaries, however, have their openings between the base of each pair 

 of arms ; there are four of them shaped like a horse-shoe, and of a purple 

 color, which renders them visible from above, as seen in the figure. 



Order 3. Cllkkjrada. This order (also named Ctenophora br 

 Eschscholtz^ is named from its organs of motion. Avhich consist of a series 

 of fiat phosphorescent vibrillse, arranged longitudinally upon the surface of 

 the body, along the eight ribs, and by the action of which progression is 

 effected. These vibrilla? are arranged with their fiat 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. Cestian venei^is has a ribbon-shaped body, the two 

 margins of which are fringed with beautifully colored phosphorescent 

 vibrillie, which at night give the animal the appearance of a band of fiame, 

 as it moves through the water. It attains the length of three or four 

 feet. 



Order 4. CirrictRada. Tlie form is discoidal, and there is an internal 

 subcartilaginous discoidal skeleton, which distinguishes them from the 

 Pulmonignida. In Porj?ifa {j^I. ~6,nff. SS) tlie margin is fringed with 

 stout claviform tentacles, provided with three i-anges of pedunculated 

 glands or suckei*s. The stomachal pedicle is large, and smrounded by 

 numerous tentaculiform cirri, by means of which locomotion is effected. 

 These bear some resemblance to the tentacles of the Actinia?, to which 

 Blainville thinks the order has some affinities. In YeleUa ( Y. spirans, 

 Forsk., pL 76. ßg. S4"), besides an oval cartilaginous skeleton, there is a 

 vertical process arising from it which supports a crest-like membrane. 



Order 5. Physograda. This order was called Hydrostatic Acalephae 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-ve«sels, 

 which cause the animal to float. Phymlia physalis, Linn, [ph 77, iig. 1), 

 possesses stin^ino: qualities ; it inhabits the Gulf of Mexico and the Atlantic, 

 and is known to sailors as the Portuguese man-uf-war. The air-vessel is 

 very lar^e. and has a small aperture at each end, from which the air can be 

 234^ 



