. Elements of biology, with special reference to their rôle in the lives of animals. Biology; Zoology. THE ORDER AMONG ANIMAL TYPES lOI ing cell termed a cnidoblast. The cnidoblast contains a coiled barbed organ which is employed in defense but more especially in the capture of its food. The ectoderm contains cells which exaggerate the property of irritability and function as a rudimentary nervous system. In this and in other respects the phylum marks a distinct advance over the phylum Porifera. Three classes are recognized: Class I. HYDROZOA (Fig. 33A and B). Attached or free swimming forms.
. Elements of biology, with special reference to their rôle in the lives of animals. Biology; Zoology. THE ORDER AMONG ANIMAL TYPES lOI ing cell termed a cnidoblast. The cnidoblast contains a coiled barbed organ which is employed in defense but more especially in the capture of its food. The ectoderm contains cells which exaggerate the property of irritability and function as a rudimentary nervous system. In this and in other respects the phylum marks a distinct advance over the phylum Porifera. Three classes are recognized: Class I. HYDROZOA (Fig. 33A and B). Attached or free swimming forms. The digestive cavity is undivided. Examples are the fresh COELENTERATA. ECTODERM ENDODERM TENTACLE NEMATOCYST CASTROVASCULAfi CAVITY FIG. 33^. HYDROZOA-HVDRA (WALL CUTAWAY) water Hydra, the composite attached Hydroids, mostly marine, found usually attached to rocks or debris, and very small free swim- ming forms shaped like umbrellas, known as Medusae, which are in reality the free swimming stages of the Hydroids. Class II. scYPHozoA (Fig. 34). The Jelly Fishes. Free swimming forms shaped like umbrellas. Some have stalks and attach to plants or other objects. These animals contain a very high proportion of water and if stranded in the sun soon evaporate to a residue that. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Buchanan, James William, 1888-. New York, London, Harper & brothers
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