320 ORGANS OF DIGESTION*. 



yellow perforated disk capable of seizing and conveying to the 

 central mouth of the polypus the smaller crustaceous or mol- 

 luscous animals brought within their reach. The most com- 

 plicated and most isolated forms of the polypi, or digestive sacs 

 of zoophytes, are the free, locomotive actinia, destitute of a 

 calcareous axis, and where the muscular and nervous sys- 

 tems, and the organs of digestion, generation, and respira- 

 tion are already distinctly developed. Strong muscular 

 bands surround the coriaceous external contractile covering 

 of the body, and others extend vertically to the spreading flat 

 base ; a thick muscular sphincter, to enclose all the delicate 

 parts of the disk, surrounds the upper and exterior margin^ 

 and another the entrance of the stomach ; and numerous ver- 

 tical muscular partitions, extending from the upper disk to 

 the base of the actinia, and from the exterior skin inwards to 

 the gastric cavity, divide this peripheral space, as in most of 

 the higher zoophytes, into numerous genital compartments 

 occupied by the long, white, convoluted, filiform ovaries, or 

 gemmiparous sacs, attached to the inner free margin of mem- 

 branous alternate folds extending inwards from the skin. 

 The capacious stomach, provided with a muscular and mucous 

 coat lined with vibratile cilia as in other zoophytes, and 

 striated with vertical opaque bands and plicae, occupies the 

 axis of the body, and communicates as in other highly-or- 

 ganized polypi, with the genital cavities below. These lateral 

 cavities between the stomach and the skin, communicate 

 with each other, and with the numerous muscular conical 

 tubular tentacula which are lined internally with vibratile 

 cilia and are perforated at their free apex, like the tubular 

 feet of higher radiata : so that every part of the actinia is 

 capable of being bathed and distended with the surrounding 

 element like a respiratory organ, and the stomach is easily 

 protruded from the mouth by the distension of the genital ca^ 

 vities behind with that fluid. The actinia, like the hydra, free 

 and unfettered by a solid axis, stretches its elastic body over 

 prey many times larger than itself, and by the great digestive 

 powers and copious secretions of its most capacious stomach, 

 it quickly extracts nourishment from all kinds of animal sub- 

 stances, living or dead, which are brought within the reach 

 of its adhesive poisonous secretions and its expanded tenta-^ 

 cula by the ceaseless motions of the tide. The sand, gravel) 



