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 
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- 
fect 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 niollus- 
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 
