GENERAL STRUCTURE OF ACTINIA. 75 



capability of destroying their victims. Their food generally consists of 

 crabs or shell-fish, animals apparently far superior to themselves in 

 strength and activity ; but even these are easily overpowered by the 

 sluggish yet persevering grasp of their assailant. No sooner are the 

 tentacles touched by a passing animal than it is seized, and held with 

 unfailing pertinacity ; the arms gradually close around it ; the mouth, 

 placed in the centre of the disk, expands to an extraordinary size ; and 

 the creature is soon engulfed in the digestive bag of the Actinia, where 

 the solution of all its soft parts is rapidly effected, the hard undigestible 

 remnants being subsequently cast out at the same orifice. 



(166.) The Actiniae possess the power of changing their position: 

 they often elongate their bodies, and, remaining fixed by the base, 

 stretch from side to side, as if seeking food at a distance : they can 

 even change their place by gliding upon the disk that supports them, or 

 detaching themselves entirely, and swelling themselves with water ; they 

 become nearly of the same specific gravity as the element they inhabit, 

 and the least agitation is sufficient to drive them elsewhere. When they 

 wish to fix themselves, they expel the water from their distended body, 

 and, sinking to the bottom, attach themselves again by the disk at their 

 base, which forms a powerful sucker. 



(167.) From the above sketch of the outward form and general 

 habits of these polyps, the reader will be prepared to examine their in- 

 ternal economy and the more minute details of their structure. On 

 examining 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 aperture of the 

 mouth, is found to coat the surface of the stomach itself : this epidermic 

 secretion forms, in fact, a deciduous tunic, that the creature can throw 

 off at intervals. On removing this, the substance of the animal is found 

 to be made up of fasciculi of muscular fibres, some running perpen- 

 dicularly upwards towards the tentacula, while others, which cross the 

 former at right angles, pass transversely round the body ; the meshes 

 formed by this interlacement are occupied by a multitude of granules, 

 apparently of a glandular nature, giving the integument a tuberculated 

 aspect : these granules are not seen upon the sucking-disk at the base. 

 The tentacula are hollow tubes, composed of fibres of the same descrip- 

 tion. 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, somewhat modified in texture. 



(168.) On making a section of the animal, as represented in fig. 36, 

 the arrangement of these parts is distinctly seen, a being the muscular 

 integument ; 6, the tentacula, formed by the same fibrous membrane ; 

 and c, the stomach. Between the digestive sac, c, and the fibrous ex- 

 terior of the body, a, is a considerable space, d, divided, by a great 

 number of perpendicular fibrous partitions, I, into numerous compart- 



