. Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote. 378 anterior end of the body (Ccf)halotrocJia, , larva of Polynoe). Sometimes there are two rows, one at each end of the body, con- stituting a prseoral and perianal ring (Telotrocha, , Sjjio-Nephtliys- larvct). In addition to these two rings of cilia, incomplete rings may also be present on the ventral surface (Gastrotroclia), or both ventrally and dorsally (AmpMtrochoi). In other cases one or more rows of cilia surround the middle of the body (Mesotrocha), while the te
. Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote. 378 anterior end of the body (Ccf)halotrocJia, , larva of Polynoe). Sometimes there are two rows, one at each end of the body, con- stituting a prseoral and perianal ring (Telotrocha, , Sjjio-Nephtliys- larvct). In addition to these two rings of cilia, incomplete rings may also be present on the ventral surface (Gastrotroclia), or both ventrally and dorsally (AmpMtrochoi). In other cases one or more rows of cilia surround the middle of the body (Mesotrocha), while the terminal rings (prjeoral and perianal) are absent (Telepsavus-Chcetop- terus larvci) (fig. 306). Many larvae are provided with long pro- visional seta?, which are later replaced by the permanent structures (Metachceta). In spite of their great diversity of form the Chaetopod larvae can in their later development also be reduced to the type of the larva of Loven. Relatively few forms, as for instance the transparent Alciopidcr, live at the surface (pelagic animals); most of them live near the coast. Numerous forms descend into the deep sea. Many have the power of emitting an intense light, especially species of the genus Chce- topterus which emit light from their an- tennse and appendages. The elytra of Polynoe, the tentacles of Polycirrus, and the integument of certain Syllidce, are also phosphorescent. Panceri* has shown that the seat of the phosphorescence is in unicellular cutaneous glands, which, in Polynoe, were proved to be in communi- cation with nerves. Sub-order 1. Errantia. Free-swim- ming, predacious Polycha'ta. The pnestorniuni always remains in- dependent and forms, with the oral segment, a well-marked head which bears eyes, tentacles, and usually tentacular cirri. The parapodia are much more developed than in the Tubicolce, and, together with their very variously shaped setae, serve as oars. The anterior portion of the pharynx can be protruded as a proboscis and is
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