34 ZOOLOGY. 



words of Dana, " within the polyp, as completely as the skull of an animal 

 beneath its fleshy covering. All corals are more or less cellular, and 

 through these cellules the animal tissues extend." In some, however, the 

 coral is exposed, as when the increase takes place by a terminal secretion 

 upon a separate stem, when the apex alone is living, and as the stem 

 increases in length the part below dies. This increase above and death 

 below are common in most corals, and to this the great masses of coral are 

 attributable. According to Dana, a solid dome of Astr^a, twelve feet in 

 diameter, has a living exterior of only a half or three fourths of an inch in 

 thickness. 



The classification adopted here is chiefly that of James D. Dana, as given 

 in his magnificent work on Zoophytes, the result of his labors in the United 

 States Exploring Expedition. The characters of the families are in most 

 cases condensed from the same work. 



The Order Actinoida includes not only the flower-shaped genera, like 

 Actinia {pi. 77,Ji(/s. 5, 6), which do not secrete a coral, but also numerous 

 coralligenous genera. The name of this order, from the Greek axnv, a 

 ray, is in allusion to the radiated arrangement of the tentacles, which, 

 when expanded, in many cases resemble the petals of a flower. When 

 contracted this resemblance disappears, and the mass may be compared to 

 a lemon in shape. Lesueur has described a species {A . marginata) from 

 Massachusetts Bay. (Jour. Acad. Nat. Sci. i. 172.) 



The Actiniae are found in the sea, attached to stones, submerged timber, 

 &c. They have the power of detaching themselves and floating, and 

 of creeping slowl}^ upon their flat base, at the rate of about two inches in 

 an tiour. The texture of the exterior is either fleshy or coriaceous, the 

 surface slimy, smooth, or tuberculous, and very sensitive. The mouth is 

 simple, and fringed by the tentacles. These organs being tubular, they are 

 expanded by having water forced into them, and when they contract, the 

 water is ejected through a minute terminal j)erforation. The tentacles of 

 some species resemble the Acalephae in having a stinging powgr. 



The interior of the Actinias is taken up with the stomach, which is a 

 simple sac, of which the mouth is the opening, and extending nearly to the 

 base of the animal, where it communicates with the visceral cavity, 

 occupying the sjjace between the stomach and the exterior wall. The 

 cavity is provided with a series of vertical muscular partitions, more or 

 less perfect, which extend from the exterior wall to the stomach, so that a 

 transverse section of the animal would resemble a wheel, of which the nave 

 would represent the stomach, and the spokes the visceral partitions. 



The Actiniae feed upon fish, crabs, shell-fish, &c., the shells and other 

 indigestible parts being ejected from the mouth after a period of ten or 

 twelve hours. A large individual sometimes accidentally swallows a smaller 

 one, but the latter is usually cast out unharmed, as in the case of the 

 Hydra. The objects swallowed are sometimes as large as the Actinia 

 itself in a state of repose. The following account is given in G. Johnston's 

 excellent History of British Zoophytes. 



" I had once brought me a specimen of Act. gemmacea., that might have 

 238 



