. A manual of zoology. Zoology. I. HYDROZOA: SIPHONOPHORA 219 radial canals) for the distribution of nourishment received from the common tube. Then come, scattered through the colony, the covering scales, for protection, firm gelatinous plates wliich have lost the ring canal, the muscles, and the bell shape of the medusa. Food is taken by wide- mouthed _/fe(f/;;^ lubes (hy) which may be compared to polyps (fig. 58) or the manubrium of a medusa. They digest the food Ijy means of large masses of glands ('liver bands,') and send it by the central tube to all the members of the colony. At the bas
. A manual of zoology. Zoology. I. HYDROZOA: SIPHONOPHORA 219 radial canals) for the distribution of nourishment received from the common tube. Then come, scattered through the colony, the covering scales, for protection, firm gelatinous plates wliich have lost the ring canal, the muscles, and the bell shape of the medusa. Food is taken by wide- mouthed _/fe(f/;;^ lubes (hy) which may be compared to polyps (fig. 58) or the manubrium of a medusa. They digest the food Ijy means of large masses of glands ('liver bands,') and send it by the central tube to all the members of the colony. At the base are long muscular tentacles (/) from which small lateral threads depend, each ending in a brightly colored swelling, the nettle head composed of large, closely packed nettle cells. These are the cause of the nettUng, which in many species is so. Fig. 182.—American siphonophores. .4, Nanomia cara (after A. Agassiz). B, Velella meridionalis (after Fewkes). C, Diphyes praya {al\.¥e\\]Lti). severe as to be feared by man. The 'feelers' (J>) recall mouthless polyps and manubria; they are very sensitive and mobile and, while tactile, ap- parently in some cases are digestive organs. Latest to develop in the colony are the sexual bells. They are usually brightly colored and re- semble small mouthless Anthomedusae without tentacles. They but rarely {Chrysornitra) separate from the colony, but usually persist as more or less reduced sporosacs. From this it follows that the Siphono- phora afford fine examples of division of labor and of the consequent polymorphism of individuals. This can indeed be carried so far that many convey the impression of being individuals with a multiplicity of organs. The Siphonophora are all marine, and occur most abundantly in tropical seas. Sub Order I. : (Physonectfe). Float present, small; next a large series of swimming bells; then the other members of the colonv. Phy- sophora, Agalmia, Nanomia* (fig. 182). Sub Order II. CALYCOPHOR^ (
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