18 OCEAN LIFE. 



a degree of sensibility, and power of spontaneous movement, which 

 we should little anticipate from their general aspect. A cloud 

 veiling the sun will cause their tentacles to fold, a though ap- 

 prehensive of danger from the passing shadows ; contact, how- 

 ever slight, will make them shrink from the touch; and if rudely 

 assailed, they completely contract their bodies, so as to take the 

 appearance of a hard coriaceous mass, hardly distinguishable 

 from the substance to which they are attached. 



" The Actiniae, like the Hydras, possess the power of chang- 

 ing their position. They often elongate their bodies, and re- 

 maining 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 disc which supports them, or detaching them- 

 selves entirely, and swelling themselves with water, they become 

 of nearly the same specific gravity as the element which they 

 inhabit, and the least agitation is sufficient to drive them else- 

 where : when they wish to fix themselves they expel the water 

 from their distended body, and sinking to the bottom, attach 

 themselves again by the disc at their base, which forms a power- 

 ful sucker. From this sketch of the outward form of these 

 polypes, we will be prepared to examine their internal economy, 

 and the more minute details of their structure. On examining 

 attentively the external structure 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 which the creature can throw off at intervals. On remov- 

 ing this, the walls of the body are seen to be made up of fasci- 

 culi of muscular fibre, some running perpendicularly upwards 

 towards the tentacula, and others which cross the former at right 

 angles, passing transversely around the body ; the meshes formed 

 by this interlacement 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 suck- 

 ing disc at the base. 



" The tentacula are hollow tubes, composed of fibres of the same 

 description. The stomach is a delicate folded membrane, form- 



