ON POLYPS. 



tended body, and sinking to the bottom attach themselves again 

 by the disc at their base, which forms a powerful sucker. 



(57.) From this sketch of the outward form and general habits 

 of these polyps, the reader will be prepared to examine their internal 

 economy, and the more minute details of their structure. On ex- 

 amining attentively the external surface of the body, it is seen to 

 be covered with a thick mucous layer resembling a soft epidermis, 

 which extending over the tentacula, and the fold around the aper- 

 ture of the mouth, is found to coat the surface of the stomach 

 itself; this epidermic secretion forms in fact a deciduous tunic 

 which the creature can throw off at intervals. On removing this, 

 the walls of the body are seen to be made up of fasciculi of mus- 

 cular fibres, some running perpendicularly upwards towards the 

 tentacula ; and others, which cross the former at right angles, pass- 

 ing transversely round the body ; the meshes formed by this in- 

 terlacement are occupied by a multitude of granules apparently 

 of a glandular nature, which give the integument a tuberculated 

 aspect : these granules are not seen upon the sucking disc at the 

 base. The tentacula are hollow tubes, composed of fibres of the 

 same description. The stomach is a delicate folded membrane, 

 forming a simple bag within the body ; it seems to be merely an 

 extension of the ex- 

 ternal tegument, some- 

 what modified in tex- 

 ture ; it is closed infe- 

 riorly, the same orifice 

 serving both for the in- 

 troduction of food, and 

 the expulsion of effete 

 or indigestible matter. 



(58.) On making a 

 section of the animal, as 

 represented in jig. 13, 

 the arrangement of these 

 parts is distinctly seen : 

 a being the muscular 

 integument ; b the ten- 

 tacula formed by the 

 same fibrous membrane ; 

 and c the stomach, 

 which is apparently de- 



