44 CORALS. 



are placed the cells wherein the Polypes lodge. Some authors have affirmed 

 that the sea-pen swims freely in the sea; but modern observation tends to 

 throw discredit on this statement. It is usually found with its stem inserted 

 into the mud at the bottom, and those that have been kept for inspection 

 have never exhibited any capability of locomotion. Some species, when dis- 

 turbed, become highly luminous, insomuch that the statement >f Linnaeus, 

 that the " phosphorescent sea-pens cover the bottom of the sea, and there 

 cast so strong a light that it is easy to count the fishes and worms sporting 

 among them," is by no means devoid of foundation. 



Hitherto we have seen the solid part either stony or horny, 



called the skeleton or polypidom, 

 deposited within the living flesh, 

 but there are some species of 

 Anthozoa in which it forms a 

 protecting sheath to the bodies 

 of the Polypes which are lodged 

 in its interior. The elegant ag- 

 gregation of tubes called 

 The Organ-pipe Coral (Tubipora* 



Musica) is an example of such a structure 

 (Fig. 39). It consists of small cylindrical 

 tubes of a rich crimson hue, placed nearly 

 parallel, but at a short distance apart, and 

 united, at regular distances by successive 

 stages of horizontal plates, that divide the 

 FIG. 39. ORGAN-PIPE CORAL. series into ranges, or storeys, like the diffe- 



rent floors of a house supported by many 



pillars. From the mouth of each tube, in the living state, protrude the eight tentacles 

 of a starry Polype of a brilliant green colour, forming a striking contrast with the crim- 

 son polypidom. 



ActiniaB.f In the succeeding group of Polypes, while the general form 

 and structure of the Anthozoa are preserved, we find an organization much 

 more complex than we have yet encountered. In the Actiniae the tentacles are 

 very numerous, and ranged in several circles round the mouth. When ex- 

 panded, being often of gay colours, they so much resemble composite flowers, 

 such as the daisy, the marigold, and others, as to have obtained their names 

 for different species, and the term u animal flowers " for the entire group. 

 When expanded and viewed in profile, the form of an Actinia is that of a 

 short, broad cylinder, with the tentacles radiating from the upper margin 

 (Fig. 40), the base being somewhat dilated. But when the absence of light 

 or water, or any other cause, induces them to repose, the tentacles contract, 

 and the upper part of the body, by a partial inversion, closes over them, leaving 

 no trace of the place where they disappeared, except a wrinkled depression in 

 the centre. In this condition their shape is, more or less, that of a bell, as 

 may be seen in the figure (Fig. 40). 



When still more firmly closed, the creature looks like nothing but a rounded 

 lump of fleshy substance, plastered on the rock (Fig. 41, ) ; but as the animal 



* Tubus, a tube ; porus, a pore. f d/cri?, aktin, a ray. 



