Page:The American Cyclopædia (1879) Volume V.djvu/344

 34:0 OOKAL food. Fig. 2 represents the coral of a single polyp, one of the larger simple kinds, reduced to one fourth its natural size. When alive the whole corallum was concealed by the fleshy FIG. 2. Fungia echinata. exterior; the mouth was situated over the middle portion of the median furrow from which the calcareous plates radiate outward ; and these radiating calcareous plates of the coral were secreted between pairs of fleshy plates, as stated above. Fig. 3 represents one of the branching corals; in the living state each little prominence was the interior of a separate flower-like polyp. Coral polyps, be- sides producing eggs and young like other ani- mals, generally multiply also through a pro- cess of budding which is closely like growth by buds in the vegetable kingdom. A new polyp commences as a mere prominence on the side of an old one ; soon the mouth and tenta- cles appear; then both continue growing, each adding to the calcareous accumulation within, FIG. 8. Branching Coral. and each sending forth new buds to be de- veloped into new polyps. According to the manner in which the buds develop the mass receives its shape. In some species they branch out into tree-like forms from the buds putting forth laterally. In many species of the madrepore family each branch terminates in what is called the parent polyp, this ter- minal polyp continuing to grow on and at the same time making new polyps for the sides of the branch by the process of budding. In a few species of other kinds each polyp forms a separate branch, at the teraiination of which it is seated; at these extremities the growth goes on, while the stem below is left behind dead. Other species, in which the polyps form massive corals, put forth the young pol- yps in the spaces which are produced between the older ones as these extend upward, or they make new ones by a subdividing of an old pol- yp ; thus keeping the hemispherical form sym- metrical, till in a single astrsea dome a diame- ter of even 12 ft. has been attained, and the polyps, each occupying a square half inch only, have increased to more than 100,000 in num- ber. Many polyps are of still smaller dimen- sions. A porites of the same size should con- FIG. 4. Meandrina (Diploria) cerebriformis. tain, according to Prof. Dana, more than 5,500,000 individuals. The genus is often met with over the coral reefs, in rudely shaped hil- locks sometimes measuring 20 ft. across. Fig. 4 represents a kind, related to the astraeas, called brain coral, in allusion to the meander- ing furrows over the surface. Here, instead of each polyp having a separate cell with its mouth over the centre of it, there are a large number of polyps coalesced along a single fur- row, many mouths being visible in the living meandrina along the bottom of the furrow, and a row of tentacles along either side. In addi- tion to the hemispherical forms seen in the star coral (astrcea) and the brain coral (meandrina), and the madrepore shrubs and trees, Prof. Dana remarks that "some species grow up in the form of large leaves rolled around one another like an open cabbage, and cabbage coral would be no inapt designation for such species. Another foliated kind consists of leaves more crisped and of more delicate structure, irregularly grouped; lettuce coral