﻿April, 1857.] 



ELLIOTT SOCIETY. 



Ill 



adult, — the cavity of the bell is, so to speak, hollowed out from 

 the original substance of the bud — and the proboscidiform digestive 

 cavity, is from the first enclosed by a parenchyma which becomes 

 gradually metamorphosed into a moveable disciform or campanu" 

 late organ of motion. The lower aperture of the bell, which, in 

 the adult is usually guarded by the vail, appears to be pierced 

 through this original parenchyma, and the tentacula never origi- 

 nate near the attached base of the gradually growing proboscis, 

 but on the contrary, near what is to be its free extremity. Now, 

 a reference to Van Beneden's figures of the development of Cam- 

 panularia, which, I think, in one of our species I have been able 

 to confirm, will show a mode of growth which in some respects is 

 entirely the reverse. There the proboscidiform digestive cavity 

 is early conspicuous as a free projecting knob, and is not over- 

 arched by the disk until some time after the Medusa becomes 

 free, in several species. The tentacula, instead of originating 

 near the free extremity of the proboscis, originate near its base — 

 and that organ, instead of being from the beginning covered by the 

 disk, is only gradually over-arched by it. And lastly, the aper- 

 ture of the bell, instead of being formed by piercing the paren- 

 chyma of the bud, is formed by the border of the outgrowing 

 lateral fold or disk which in this case is always free. The result 

 is, that in its early stages, just before its independence, the young 

 Campanularian Medusa bears an extremely close resemblance at 

 first sight to the mere hydroid polyp from which it is bred, which is not 

 the case among the Tubularina. Now, a reference to the descrip- 

 tion of the mode of growth exhibited by the larva of Jleginopsis 

 Mediterranea, and that described by myself in the bell of an Oce- 

 ania,* it will be seen at once that it is essentially the same as that 

 of Campanularia, and this corresponds to the structural affinities 

 of the Aeginidse, which every one, I believe, considers more closely 

 allied to the Thaumantiads than to the Sarsiadae and the like. 



But these differences are not confined to the Larval stages alone. 

 The adult Medusse, so far as known, belonging to these two groups, 

 appear to be distinguished by general form and structural pecu- 

 liarities in such a manner, that we must consider the Sertularian 

 group inferior. I might notice, however, beforehand, that embry- 

 ologically they appear to be lower, for while, if anything, their 

 polyps are more complicated, and vegetative character more prom- 



* This, I have since satisfied myself, is the parasitic young of a Cunina. See 

 the descriptions of Turritopsis and Cunina below. 



