The porifera and coelentera . >ecomes continuous with the ectoderm of the zooids, and form a circular operculum over them when retracted than in this sheet, ectoderm, mesogloea, and endodermbear to one another the relations usual in Hydrozoa. The hydroids (Fig. 13) are of two kinds. The gastrozooids, the THE HYDROMEDUSAE nutritive zooids of the colony, may possess capitate tentacles(Millepora), generally four, six, or twelve in number, or maybe entirely devoid of tentacles (Astylus). The endoderm cellsnear their mouths are swollen and secretory. The dacfylozo
The porifera and coelentera . >ecomes continuous with the ectoderm of the zooids, and form a circular operculum over them when retracted than in this sheet, ectoderm, mesogloea, and endodermbear to one another the relations usual in Hydrozoa. The hydroids (Fig. 13) are of two kinds. The gastrozooids, the THE HYDROMEDUSAE nutritive zooids of the colony, may possess capitate tentacles(Millepora), generally four, six, or twelve in number, or maybe entirely devoid of tentacles (Astylus). The endoderm cellsnear their mouths are swollen and secretory. The dacfylozooidsare generally devoid of mouths, and either have (Millepora) orlack (Stylaster) capitate tentacles; their endoderm cells are notenlarged. In some genera two kinds of dactylozooids are dis-tinguishable by size and position (Spinipora). Both forms of hydroid have strong retractor muscles, and. ? 1 \Wr^
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Keywords: ., bookcentury1900, bookdecade1900, booksubje, booksubjectctenophora
