. Elementary text-book of zoology. Zoology. 310 alimentary canal. Hooks and suckers are absent. A cerebral ganglion is present. The Turbellaria usually possess an oval flattened body, and reach only a small size. The uniform ciliation of the body is connected with their existence in fresh and salt water, beneath stones, in mud, and even in damp earth. Only in exceptional cases do we meet with apparatuses for adhering, viz., small hooks and suckers. The skin consists of a single layer of cells, or of a finely granular layer containing nuclei, which is sup- ported by a stratifi
. Elementary text-book of zoology. Zoology. 310 alimentary canal. Hooks and suckers are absent. A cerebral ganglion is present. The Turbellaria usually possess an oval flattened body, and reach only a small size. The uniform ciliation of the body is connected with their existence in fresh and salt water, beneath stones, in mud, and even in damp earth. Only in exceptional cases do we meet with apparatuses for adhering, viz., small hooks and suckers. The skin consists of a single layer of cells, or of a finely granular layer containing nuclei, which is sup- ported by a stratified basal membrane, and covered externally by a special homogeneous membrane bearing cilia and comparable to a cuticula. Peculiar integumentary structures, which have the form of rods or spindles, and, like the nematocysts in Coelenterata, take their origin, in cells, are not unfre- quently present. Various pigments are also often found embedded in the epi- dermis, and of these pigments the green- coloured vesicles, in Vortex viridis for example, which are identical with chlo- rophyl corpuscles, are specially worthy of remark. Pear-shaped mucous glands are also present. Beneath the conspicu- ous basement membrane which supports the epidermis lies the dermis. It con- tains the strongly developed derma] muscular system embedded in a connec- tive tissue layer formed of round, often branched cells. A body cavity between FIG. 247. — Alimentary canal and ner- , , , n -, ,. vous system of af«-«>rf«wa» &,*•». the bodv wal1 and the alimentary canal,. rgii (after Graff). G, the two is? as a ruie) absent : it may, however, cerebral ganglia with two eye spots; st, the two lateral nerve in many cases be recognised as a system trunks; L '.alimentary canal with of lacunse or as a continuous cavity mouth and pharynx. surrounding the alimentary canal. The nervous system consists of two ganglia connected by a com- missure, and giving off nerve fibres in various directions ; of the
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1884
