Page:Popular Science Monthly Volume 1.djvu/272

260 the branches are minute cells (indicated by the fine dots in the woodcut), each of which was the seat of one of the little hydra-like animals (in this case not more than the fourth of a line long), and usually with short tentacles spread out star-like.

"We will now pass to the true polypes. These may be divided into those which secrete coral and those which do not. The latter

have soft, leathery bodies, and live attached to stones and other substances upon the sea-bottom, by a basal, sucker-like disk. They have the power of locomotion by contraction and expansion of the muscles of the disk. But the coral-making polypes are fixed to the stone which they create, and which is part of themselves. The polype is the living part of the coral, the gelatinous mass which

fills the radiating cells upon the coralline surface. It consists of a sac or stomach, and an enveloping membrane. An opening from the stomach outward is the animal's mouth. This is surrounded by tentacles, which by their motion aid in bringing to it currents of water in which floats its food, and of the solid matters of which it constructs its calcareous skeleton." In the polype, the stomach or digestive sac, with its appendages, constitutes the whole animal. Into the stomach