Chap. H. HABITS OF AURELIA. 75 



of each oral appendage are brought together very closely and soldered along the 

 edges, for nearly their whole extent, leaving, however, at short distances, small open- 

 ings between the marginal lobules, which arise from the circumstance, that the 

 junction of the edges is not continuous for the whole length of the margin, but 

 remains gaping at intervals. In Aurelia, the margins of the oral appendages are 

 also brought into close proximity as it grows older, each appendage folding along 

 its middle line, and thus inclosing a continuous channel for its whole length, but 

 the edges are not soldered. In many other Discophoras, the oral appendages resemble 

 those of Aurelia, with this difference only, that the appendages are not so closely 

 folded, and in others they remain broadly open, as, for instance, in Cyanea and 

 allied genera. This latter structure recalls an earlier condition of the young Au- 

 relia, as represented in PI. X^ Fi(/s. 39, 40, and 41, at which time the whole 

 proboscis resembles more a loose curtain surrounding the mouth, as in Cyanea, than 

 a specialized, quadripartite, oral apparatus, as exists in the higher Semasostomejfi and 

 in the Rhizostomeas. Another point of resemblance between Aurelia and some of 

 the Rhizostomeae, may be traced in the mode of ramification of the chymiferous 

 system, which in Rhizostoma and Polyclonia consists, also, of straight, simple tubes, 

 alternating with more or less complicated anastomoses, while in the others it forms 

 broad pouches. TIius Aurelia appears as a standard, for the appreciation of the 

 relative rank of all the principal representatives of the order of Discophora?, to 

 which it belongs, so far as their natural affinities and their respective standing, in 

 their adult state, can be determined by a compaxison with the successive stages of 

 growth of one of their highest types. 



SECTION VI, 



HABITS OF AURELIA. 



After this digression, let us now return to the special history of tlie Aurelia. 

 The appearance of these medusEe along our coast is as regular as the return of 

 the seasons, and as they live only during one summer, they may truly be said 

 to be annual animals, in the same sense as we distinguish between annual and 

 perennial plants. They make their appearance, as free swimming Medusae, towards 

 the latter part of April, when they are not yet an inch in diameter; they grow 

 rapidly during the months of May and June, when they have acquired their average 

 size, from eight to ten inches in diameter, though they are then much thinner 

 and more transparent, and their genital organs are less conspicuous, owing to their 



