ACTINOZOA. 141 



c. Tegumentary organs, 



d. Corallum or Skeleton, 



e. Muscular system and organs of Locomotion, 

 /. Nervous system and organs of Sense, 



g. Keproductive organs. 



3. Organs of M^wtrition. — The whole interior 

 of the polypes and, in the budding species, that 

 of the ccenosarc by which they are connected, con- 

 stitutes the nutritive apparatus of the Actinozoa. 



In most Zoantharia the structure and functions 

 of the polypes are best illustrated by reference to 

 the account of Actinia, above given. But in some 

 members of this order the digestive sac is rela- 

 tively much shorter than the somatic cavity, being, 

 according to Dana, little more than '2 of its length 

 in the genus Palythoa. 



So, likewise, among the Alcyonaria, the somatic 

 cavity of each polype usually appears as a long, 

 somewhat slender, tube, in the upper portion of 

 which the comparatively short stomach is, as it 

 were, suspended ; the proximal, or post-stomachal, 

 region of the body cavity becoming gradually 

 much narrowed. In the Oorgonidce, however, 

 the somatic cavity is shorter and slightly dilated 

 towards its basal extremity. 



There are two apertures to the digestive cavity of 

 every Actinozoon ; first, the mouth, and secondly, 

 the proximal or inferior outlet, which opens freely 

 into the somatic cavity. 



In many, though not all, Alcy onaria, ih.e somatic 

 cavities of the separate polypes which make up 

 the compound mass are prolonged into canals, 

 freely communicating with one another, inoscu- 

 lating, and forming a sort of aquiferous system. 



