234 



Natural History of British Zoophytes. 



motion, and are supposed to perform jthe office of breathing organs 

 by keeping up a constant current of wa- 

 ter along their surfaces, which sets in 

 towards the mouth in an invariable di- 

 rection ; and from the incessant revolu- 

 tion of particles within the mouth and 

 the gullet, observed by Professor Grant, 

 this organ seems to be also ciliated inter- 

 nally. The more especial use of the ten- 

 tacula is to arrest the prey which chance 

 floats within their reach and conduct it to 

 the mouth, — a simple aperture placed in 

 the centre of the tentacular circle, and 

 which is armless, having in no instance 

 either jaws or teeth. It is the entrance 

 into a long membranous gullet (6,) of per- e 

 feet transparency, and which can be traced through its equally 

 transparent envelope, to its termination in a somewhat globu- 

 lar and comparatively large organ placed near the curvature 

 of the body, and rendered opaque partly by the greater thick- 

 ness and fleshiness of its structure, but perhaps more so by the na- 

 ture of its contents. This is the stomach (c,) and from the side 

 of it there proceeds a narrow intestine (d,) which follows a straight 

 upward course along the side of the gullet, and opens at the aper- 

 ture of the cell by a separate orifice from which the undigested re- 

 mains of the food are ejected. There is another organ of a round- 

 ish figure appended to the bend of the intestine, which is supposed 

 by some to be an ovarium (e,) but it seems not unnecessary to re- 

 mark, that this appropriation of it to the generative function has per- 

 haps no better proof than what is derived from a similarity of posi- 

 tion between it and the supposed ovarium of the compound mollus- 

 ca. It is, I presume, the organ which Blainville says he is willing 

 to believe performs the functions of the liver,* an opinion in which 

 I am disposed to concur. 



No trace of a nervous or vascular system of any kind has been 

 detected, nor is there any organ of sense, but the polypes are 

 notwithstanding very, sensible of external impressions.t When 



currents had been previously observed, but had been attributed erroneously to 

 the movements of the tentacula. 



* Manuel d'Actinologie, p. 72 Fig. 2 represents the polype of Vesicularia 



imbricata highly magnified. It is copied from Thompson's Zool. 111. Memoir, 

 v. pi. 1, fig. 4. 



f " But as we perceive, in these animals, phenomena which take place by 

 the medium of nerves in animals of a more elevated order, that is to say, sensi- 



4 



