BICIDIUM. 



15 



Fig. 13), instead of a circular opening. The mouth is also a 

 little out of centre, rather nearer one end of the disk than the 

 other. These facts are interesting, as showing that the ten- 

 dency towards establishing a balance of parts, as between an an- 

 terior and posterior extremity, a right and left side, is not forgot- 

 ten in these lower animals, though their organization as a whole 

 is based upon an equality of parts, admitting neither of pos- 

 terior and anterior extremities, nor of right and left, nor of 

 above and below, in a structural sense. This animal also pre- 

 sents a seeming anomaly in the mode of formation of the 

 young tentacles, which always make their appearance at the 

 posterior extremity of the longitudinal axis, the new ones being 

 placed behind the older ones, instead of alternating with them as 

 in other Actinias. 



JBicidium. (Biddium parasiticum Ag.) 



The Bicidium (Fig. 14) , our parasitic Actinia, is to be sought 

 for in the mouth-folds of the Cyanea, our common large red 

 Jelly-fish. In any moderate-sized specimen of the latter from 

 twelve to eighteen inches in diameter, we shall be sure to find 

 one or more of these parasites, hidden away among the numerous 

 folds of the mouth. The body is long and tapering, having an ap- 

 erture in the extremity, the whole animal being Kg. i4. 

 like an elongated cone, strongly ribbed from 

 apex to base. At the base, viz. at the mouth 

 end, are a few short, stout tentacles. Tliis Ac- 

 tinia is covered with innumerable little trans- 

 verse wrinkles (see Fig. 14), by means of which 

 it fastens itself securely among the fluted mem- 

 branes around the mouth of the Jelly-fish. It 

 will live a considerable time in confinement, at- 

 taching itself, for its whole length, to the vessel 

 in which it is kept, and clinging quite firmly if 

 any attempt is made to remove it. The general 

 color of the body is violet or a brownish red, 

 though the wrinkles give it a somewhat mottled appearance. 



Pig. 14. Bicidium parasiticum; natural size. 



