12 DISCOPHOR^. Part III. 



using different means in studying the subject from different points of view, each 

 requiring a special training. Under these circumstances, it has occurred to me that 

 an attempt at combining into one S3'stematic whole the various results ol^tained 

 during a jirolonged investigation of one of our Acalephs might not be useless in 

 showing what may be done in studying steadily, for a great many years in suc- 

 cession, one of our most common species. I j^ropose, therefore, in this chapter, to 

 make the attempt to present one of our most common Discophoroa, the Aurelia 

 flavidula of Peron and LeSueur, in aU its different aspects. I hope thus not only 

 to revive the interest for a more careful investigation of our common animals, whose 

 study seems now universally neglected, but also to show that the harvest a student 

 of nature is likely to reap cannot fail to be richer, when he turns his attention 

 to common objects, Avhich he }nay easily obtain at all seasons, than it can be 

 through seeking opj)ortunities of describing new species. 



Following what seems a natural course, I shall first give an account of the 

 formation and growth of our Aurelia, considered morphologically as well as micro- 

 scopically ; next, I propose to consider the structvn-e of the adult, and to trace 

 its homologies; then, to examine its habits, its geographical distribution, and its 

 affinities ; and, finally, to analyze all the data thus obtained, with a view to 

 improving the classification of Acalephs in general. 



The genus Aurelia, to which this species lielongs, was first characterized by Peron 

 and LeSueur, in 1800. Prior to that time the species belonging to it were included 

 in one genus, not only with all the other Discophorje, but even Avith all the Aca- 

 lejihs then known. Aurelia flavidula, to which I intend to devote particular attention 

 here, is the North American representative of Aurelia aurita, the most common 

 Medusa of the coast of Europe. ' The latter species, having been described by 

 most writers on Acalephs, and minutely illustrated by Ehrenberg in a special paper, 

 affords a most desirable opportunity for extensive comparisons, rarely to be had 

 in investigations upon this class of animals. 



SECTION II. 



FORMATION AND GROWTH OF AURELLi FLAVIDXILA, INCLUDING COMPARISONS WITH 



CYANEA ARCTICA. 



The Egg of Aurelia flavidula. Nothing is known of the manner in which 

 the egg-cell originates ; Avhether it is one of the cells of the ovary set free to 

 act in an independent manner, or develops from a fluid mass lying in the inter- 

 stices of the cells, has never been determined by direct observation. 



