. Elementary text-book of zoology, general part and special part: protozoa to insecta. Animals. 310 PLATIIIELMINXnES. alimentary canal. Hooks and suckers are absent. A cerehral (jangVion is ])resent. The Turhellaria 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
. Elementary text-book of zoology, general part and special part: protozoa to insecta. Animals. 310 PLATIIIELMINXnES. alimentary canal. Hooks and suckers are absent. A cerehral (jangVion is ])resent. The Turhellaria 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 strvxctures, 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 Avith chlo- rophyl corpuscles, are specially wor'thy 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 dermal muscular system embedded in a connec- tive tissue layer formed of round, often l)ranclied cells. A body cavity between the body wall and the alimentary canal, is, as a rule, absent; it may, however", in many cases be recognised as a system of lacunne, or as a continuous cavity 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 these, two especially large lateral trunks run backwards, one on either side (fig. 247). The latter are connected at regular intervals by delicate transverse trunks. In a number of dendroco^l
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectanimals, bookyear1892
