﻿April, 1857.] 



ELLIOTT SOCIETY. 



117 



Aeginopsis, (Miiller, Kolliker and Gegenbaur,) Stenogaster* (Kol- 

 liker,) and Cunina, (See p. Ill, note,) it is in every case a homog- 

 ony or direct metamorphosis, in which every individual hydra is 

 metamorphosed into a perfect medusa of low type. I have shown 

 that gemmation takes place, but the larvae are never fixed and 

 swim freely, or attach themselves as parasites to the bell cavity of 

 other medusae, and every bud assumes first the form of the hydra, 

 from which it directly passes to that of the medusa along with the 

 stock-hydra, from which it is bred. There the original hydra and 

 all its buds become medusae. A strong analogy exists, therefore, 

 between this state of things and the communities of medusa* 

 among Siphonophorae such as Forskalia, where a considerable 

 number of the parts possess circulatory tubes, and though much 

 modified, appear to be referable to the medusa stage of growth, as 

 well as the sexual buds. Add to this that in both instances the 

 communities are free, that is, in the latter case attach themselves 

 at will. But here the analogy ceases. The Siphonophorae de- 

 velop the medusae after the Tubularian method, the disk inclosing 

 the digestive trunk from the first. The contrary is the case in the 

 Aeginidae, as I have shown already in this volume. In the larval 

 Cunina (PI. 6 and 7.) which I have there described, the disk grows 

 out from the base of the hydra as a circular fold and growing down- 

 ward gradually overarches the gradually contracting siphon of the 

 digestive cavity, so that the disk does not come wholly to include 

 the digestive trunk until after it has attained its activity as a 

 swimming organ. The digestive siphon gradually retires also 

 within the vailed opening of the disk, having been originally 

 without it; the same is the case with Campanularia, and exactly 

 the reverse is the case with the Tubularians, where the digestive 

 trunk is always originally wholly within the vailed rim of the bell 

 and does not come without until the animal is either completely 

 developed or nearly so. A glance at Miiller's figures of the de- 

 velopment of Aeginopsis Mediterranean (Miiller's Archives, 1651, p. 

 272) will show that there the disk must grow in the same manner. 

 From this correspondence, therefore, in the growth of the swim- 

 bell or disk, united with their structural affinities, I include the 

 Aeginidae in the Sertularian group. 



To those who believe that there is a deep gulph between alter- 



*The resemblance of Stenogaster to the Larva I have described in this volume, 

 pp. 77-79 is so great that it will very probably, I think, turn out to be a Cunina or 

 Aegineta. See below Cunina. 



