^Pedicellina^ ^P. americana^ [pg190] TERMS USED IN DESCRIBING POLYZOA ^Avicula´ria^: Specifically modified zoœcia, resembling a bird's head, found only in the /Cheilostomata/. ^Brown bodies^: Brown pigment-masses contained in the zoœcia and derived from the breaking down of the polypides. ^Lo´phophore^: The disk bearing the mouth and circlet of ciliated tentacles. ^Orifice^: The open end of the zoœcium. ^Ovicell^: The receptacle in which the eggs develop. ^Pe´ristome^: The ridge around the orifice of cell. ^Po´lypide^: The parts of the animal within the zoœcium. ^Vibra´cula^: A lashing filament, or specifically modified zoœcia, found only in the /Cheilostomata/. ^Zoa´rium^: The whole colony. ^Zoœ´cium^: The body-wall of a single individual. [pg191] POLYZOA Among the numerous objects to be found on the beach at low tide are the /Polyzoa/, of which there are said to be seventeen hundred named species of the marine forms. These little animals, although so plentiful, are inconspicuous, and it may be said that their very existence is not known to those who are not professed naturalists; yet they are easy to see, incrusting with a delicate calcareous lacework the surface of stones and shells and seaweeds in the tide-pools, and hanging from the rocks like branches of delicate seaweeds. There is hardly a frond of even the fine red algæ on which cannot be found the little tube holding shelly saucers, or the creeping stems or branches of polyzoans. Any one of these little masses, when examined with a pocket-glass, will surprise one with its delicate and beautiful structure. This class of animals is also called /Bryozoa/, and certain species have the common names of sea-mats and corallines. They are broadly divided into two groups, namely, the erect and the incrusting forms. Those having tree- or plant-like shapes resemble seaweeds, while the colonies which spread over stones, shells, and algæ resemble moss, hence the name /Bryozoa/ (moss-animals). Both groups have the general appearance of hydroids, because, like them, they are colonies having plant forms and having their organisms inclosed in cup-like sheaths. The resemblance, however, is but a superficial one, for the /Polyzoa/ have a much higher organization, each animal of the colony being a separate and distinct individual. They can easily be distinguished by the hair-like processes on the tentacles. The ciliated tentacles and complete alimentary system are the conspicuous differences between these colonies and those of the hydroids.