TABLE SHOWING THE CLASSIFICATION OF THE HYDROZOA DESCRIBED IN THIS CHAPTER Class =HYDROZOA= Order =LEPTOLINIÆ= (/Branched colonies or shrub-like communities of hydroids; some permanently fixed, others liberate swimming-bells/) Suborder =ANTHOMEDUSÆ= (/Zoöids not covered by protective sheath; umbrella of medusæ strongly arched; egg-sacs in manubrium/) Division TUBULARIANS (/Without polyp-cups/) Genera and Species ^Clava leptostyla^ ^Hydractinia polyclina^ ^Coryne mirabilis^ ^Sarsia^ ^Eudendrium ramosum^ ^Tubularia indivisa^ ^T. Couthouyi^ ^Parypha crocea^ ^Corymorpha pendula^ ^Hybocodon prolifer^ ^Pennaria tiarella^ ^P. gibbosa^ ^Bougainvillea superciliaris^ Suborder =LEPTOMEDUSÆ= (/Zoöids covered with cup-like sheaths; umbrella of medusæ thin and not very convex; egg-sacs in line of radial canals/) Division CAMPANULARIANS (/Polyp-cups stalked/) Genera and Species ^Obelia commissuralis^ ^Eucope diaphana^ ^Oceania languida^ ^Clytia poterium^ ^C. bicophora^ Division SERTULARIANS (/Polyp-cups sessile/) ^Sertularia pumila^ ^S. argentea^ ^S. cupressina^ Division PLUMULARIANS (/Polyp-cups on one side of branches only/) ^Aglaophemia struthioides^ ^Plumularia falcata^ Family =GERYONOPSIDÆ= ^Tima formosa^ Family =ÆQUOREIDÆ= ^Zygodactyla groenlandica^ Order =TRACHYLINÆ= (/No fixed zoöphyte stage; always free-swimming medusæ/) Suborder =TRACHYMEDUSÆ= (/Tentacles spring from margin of umbrella; manubrium long; gonads in connection with radial canals/) Genera and Species ^Trachynema digitale^ Suborder =NARCOMEDUSÆ= (/Tentacles spring from midway between summit and margin of umbrella; manubrium short; gonads in connection with manubrium/) Order =HYDROCORALLINA= (/Skeleton of carbonate of lime/) ^Millepora alcicornis^ Order =SIPHONOPHORA= (/Pelagic free-swimming colonies; exhibit extreme polymorphism of zoöids/) ^Nanomia cara^ ^Physalia arethusa^ ^Vellela limbosa^ TERMS USED IN DESCRIBING HYDROIDS ^Cœnosarc^ ("common flesh"): The fleshy axis, or organized living bond, by which the zoöids are organically united to one another. It consists of three layers: ectoderm, endoderm, and mesoderm. ^Ectoderm^ ("outside skin"): The outside one of the three organized layers of which every hydroid is composed. ^Endoderm^ ("inside skin"): The innermost layer. ^Gonangium^ ("seed-vessel"): The external horny receptacle within which the gonophores are developed. ^Gonophore^ ("seed-bearing"): A generative zoöid.