234 



Natural History of British Zoophytes. 



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

 by keeping up a constant current of wa- Fig. 2. 



ter along their surfaces, which sets in §n r 



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- & 

 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 bad 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 



