ALCYOITIMI, a genus of zoophytes, the type of a family called alcyonidm, belonging to the class antkozoa, and other asteroida, and consisting of a polype-mass with starlike pores and protrusive polypes. A. digitatum, is extremely common on the British shores, on stones, old shells, etc., in deep water. It sometimes appears as a mere crust, about the eighth of an inch in thickness, but commonly rises up in rounded cones, and often assumes forms which have procured for it the popular name of dead man's fingers, and other similar appellations. The polype-mass is gelatinous within, and covered with a sort of leathery skin, the mass being traversed by a multitude of minute canals, ter minating on the outer surface in starlike figures, which, if the whole is placed in sea water, are seen to project considerably from the surface, and appear as polypes with eight tentacula or feelers; so that what seems to be a disgusting fleshy mass in the fisher man's proves to be, when placed in its proper element, a structure of wonderful beauty and full of animal life, existing under peculiar and wonderful conditions. The manner in which the polypes protrude and retract themselves has been likened to that in which the horns of a snail are protruded and retracted. Their tentrienla are short, obtuse, and elegantly fringed at the margins. The external part of the body of the polype is a membrane so transparent, that by the employment of a magnifying glass the whole internal structure can be seen through it. This delicate membrane, however, is composed of two very thin membranes, intimately united, the outer of which increases in thickness at the base of the polype, coalesces with that of adjacent polypes, and is continuous with the common leathery skin of the polype-mass. The inner membrane retains its extreme delicacy throughout ; it extends into and lines the cell of the polype and the tube or canal which proceeds from the cell into the mass, and is thus also con tinuous with the corresponding membranes of other polypes ; for the canals divide into branches in their course from the base of the polype-mass to the surface, and the intimacy of union in the whole is increased by a fine tubular net-work which occupies the spaces between the principal canals. If a portion of an A. is irritated, not only the particular polypes immediately subjected to irritation retract themselves as to withdraw from danger, but the gradual collapse and contraction of the whole polype mass shows that the irritation has been felt through it all. The contraction of the mass is owing to a discharge of water, which the polypes, when protruded, imbibe, and which circulates through and distends the polype-mass, so that when the polypes are undisturbed, and in full activity, it has twice or three times the size which it has as we find it cast out upon the beach. The stomach of each polype is cylindrical
and beneath it is a comparatively large cavity, into which bang loosely eight twisted filaments or threads, the use of which is not well ascertained, and has been the sub ject of very different opinions among naturalists. In the gelatinous substance of the which fills the interstices of the tubular net-work, numerous crystalline calcareous spicula lie immersed, like the raphide$ (q.v.) found in the intercellular passages of some plants. They are toothed on the sides, but are of various forms, and have no organic connection with any part of the animal structure ; their only use appar ently being to impart some degree of strength to the whole. These spicula are of general occurrence in zoophytes of this order, and are secreted by the common skin of the polype-mass. The polype-mass increases- by gemnur or buds, which grow into new branches ; but the propagation of the species takes place by ora or eggs, which first appear as minute smooth warts on the membrane of the canals in the interior. The constriction of the neck, by which they grow, separates them from the parent membrane, and they move through the canal by means of very minute vibrating cilia or hairs with which they are furnished, until they reach the stomach of a polype, into which they enter, and through which they more slowly proceed till at last they are ejected by the mouth (the only opening), and committed to the waves and tides. The ova seem as if capable of feeling whilst within the parent mass, and may be observed to move back wards and forwards, and to contract their sides as if by voluntary action in their passage through the body of the polype. These wonderful phenomena of nature are the more easily observed because the ova are of a deep vermilion color, beautifully contrasting with the pure white of the polype, through the tunic of which they are seen.—One of the most remarkable known species of A., and the largest, is that called A. poculum or Neptune's cup, which was discovered by Sir Stamford Raffles upon the coral-reefs of Sumatra, and is found in the neighborhood of Singapore. It grows erect, sometimes attaining nearly 3 ft. in height and 18 in. in diameter. Specimens are now frequent in museums in this country.