HYDROZOA

the name given to a cla of Coelenterata belonging to the sub-.hylum Cnidaria; it is coincident with Hydromedusae or Craspedota, with the addition of the Acalephae. This cla includes polyps, colonies of lyps which produce medusae by budae and medusae which rise directly from the egg. The polyps, which are small in size, are generally attached permanently to foreign bodies,but sometimes as in Siphonophora, the whole colony may be free-swimming. The first polyp a umes an upstanding position termed the hydranth, which lengthens and buds until it forms a colony or hydrosome, The generative cells, which are always ripening and discharging, may arise in a variety of places, but always migrate to the ectoderm of the gonophore. H. feed chiefly on animal substances, and with few exceptions are No CeND marine organisms, 'The cla is divided into the orders Hydridae, Hydrocoral9 gate Narco medusae, and Siphonophora.