ACALEPHiE. 1 1 1 



selves, as at a and h.jig. 63.; their superficial cilia create vortices in 

 the surrounding water, v.hich carry the nutritive molecules to the 

 mouth of the young Medusa, which is now metamorphosed into an 

 eight-armed ciliobrachiate polype. The arms or tentacula are very 

 like those of the ovaria and testis in the adult. Their cilia are not 

 placed in two regular rows as in the true Bryozoa. They contain 

 clear corpuscules, arranged in regular bracelets, as in the tentacles 

 on the margin of the disc of the fully developed Medusae. The 

 whole tissue is highly contractile ; the change from the extended 

 state («, a) to the contracted one (6, 6) is instantaneous when the 

 polype is irritated. The mouth of the polype-shaped young is very 

 contractile and expansible ; they feed on Infusoria and on their in- 

 fusory-like younger brethren, one half of whose body may often be 

 seen hanging out of the mouth of the little devourer. 



The young Medusae remain in the polype state five months, from 

 September to the following February, and probably attach them- 

 selves to rocks in the more tranquil depths of the ocean during the 

 stormy months of winter. M. Sars, who confirms the preceding ob- 

 servations of Dr. Siebold, has traced the remainder of the meta- 

 morphoses of the Medusa.* The number of tentacula is augmented 

 by the development, in October, of additional ones in the interspaces 

 of the eight primitive series : the body increases, but more in thick- 

 ness than in length ; it even developes buds, which grow into young 

 polypes, with the power of completing their change into the Medusa 

 state, — that change being essentially a subdivision of the thickened 

 body of the many-armed pseudo-polype by spontaneous transverse 

 fission, at several equidistant points, into from ten to fifteen young 

 Medusae, which present the form described and figured by M. Sars in 

 1829 as a new genus of Acalephan, under the name of Strobila, 

 This most extraordinary process takes place in February. It was 

 observed by Sir J. G. Dalyell in 1835-|-, and described as one of the 

 generative phenomena of the Hydra tuba, under which name that 

 acute observer had designated the polype-like larva of the Medusa. 

 The Hydra tuba is not, however, the masked form of one, but the 

 potential aggregate of numerous Medusae. We thus see that a Me- 

 dusa may actually be generated three successive times, and by as 

 many distinct modes of generation, — by fertile ova, by gemmation, 

 and by spontaneous fission, — before attaining its mature condition. 

 When finally liberated by the third and last process they rise to 

 the surface, and swim about as small Medusae, rapidly increasing 



* Archiv. fur Naturgesch. 1841, p. 9- 



f Edinb. New Philos. Journal, vol. xxi. I8;36, p. 92. 



