512 RADIATES: ACALEPHS. 



Soon each ephyra assumes the form of the perfect jelly- 

 fish. Thus a single scyphostoma, the product of a single 

 egg, becomes a strobila, which at length divides into nu- 

 merous parts, each of which becomes a perfect jelly-fish. 



CYANEID^E. This Family contains Cyanea and its allies. 



The Genus Cyanea contains C. arctica, Per. & LeS., 

 which is one of the most magnificent of all jelly-fishes, 

 attaining a diameter of two or three feet, and with ten- 

 tacles which extend to the enormous length of twenty or 

 thirty feet. The color of the disk is bright purplish red, 

 the margin whitish with a tinge of grayish blue ; and the 

 tentacles vary from orange to deep purple. Its mode of 

 development is essentially the same as that of Aurelia. 

 It inhabits the northeast coast of North America. 



PELAGID^E. This Family comprises Pelagia, and allied 

 genera. In the mode of development, they differ essen- 

 tially from the two preceding families, inasmuch as the 

 young hatched from the egg passes directly into the 

 ephyra form. P. cyanella, Per. & LeS., Fig. 492 about 

 half the natural size, is found on the coast of Florida. 



SUB-SECTION III. 



THE ORDER OF HYDROID^E, OR HYDROIDS. 



THIS Order includes the lowest acalephs, and embraces, 

 according to Agassiz, two more or less distinct forms, one 

 of which, though having the structure of acalephs, reminds 

 us of polyps, described in the next section, and the other 

 closely resembling medusae proper ; and between these 

 there is every possible gradation. All the so-called hy- 

 droid polyps, and the naked-eyed medusas, belong to this 

 order, which is divided by the distinguished author just 

 named into eight sub-orders, forty-six families, and about 

 one hundred and thirty genera. Occurring, as they do 

 in many cases, in one stage of their existence at least, as 

 mere discolored lichen-like patches on sea- weed, stone, or 



