. Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote. 310 PLATYIIKLMINTIIES. a alimentary canal. Hooks and suckers are absent. A cerebral ganglion is present. The Turlidl'irla 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 gra
. Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote. 310 PLATYIIKLMINTIIES. a alimentary canal. Hooks and suckers are absent. A cerebral ganglion is present. The Turlidl'irla 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 Ccelenterata, 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 systern embedded in a connec- tive tissue layer formed of round, often branched cells. A body cavity between FIG. 217.—Alimentary canal and ner- ,, , , , ,, ,. Tons system of Meioetomum Ehren- the body wall and the alimentary canal, i,;->,i; (after Graff). G, the two js as a ruie absent; it rnav, however, ' cerebral ganglia with two eye . " spots; st, the two lateral nerve in many cases be recognised as a system of lacuna'', or as a continuous cavity surrounding the alimentary canal. The nervous system consists of two ganglia connected by a com- xnissure, and giving off nerve fibres in various direc
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