. Comparative anatomy and physiology. 372 COMPARATIVE ANATOMY AND PHYSIOLOGY. all but it, the members of which are always fixed when adult, a definite tissue, or collection of cells, becomes specially endowed with a contractile function, and forms muscular tissue, and a more or less regularly disposed muscular system. (For the minute structure of muscle see " Klein's Histology," chaps, viii. and ix.) In Hydra, among the Coelenterata, the only indications of muscular tissue are the branched prolongations in- wards of certain of the cells of the ectoderm (neuro- muscular cells of Klein
. Comparative anatomy and physiology. 372 COMPARATIVE ANATOMY AND PHYSIOLOGY. all but it, the members of which are always fixed when adult, a definite tissue, or collection of cells, becomes specially endowed with a contractile function, and forms muscular tissue, and a more or less regularly disposed muscular system. (For the minute structure of muscle see " Klein's Histology," chaps, viii. and ix.) In Hydra, among the Coelenterata, the only indications of muscular tissue are the branched prolongations in- wards of certain of the cells of the ectoderm (neuro- muscular cells of Kleinenberg, or, more shortly, Klei- nenberg's cells); in it the several cells of the body still re- tain their indepen- dent Fig. 158.—Larva of Holothuria tubulosa in its natural position. The arrow indicates the axis of rotation, and the cilia are seen to be arranged in a sinuous T i • i <• -T band. (From Carpenter, after Selenka.) Ill higher lOrniS the epithelial ingrowths become more independent, and in the Medusa? they become transversely striated. In these last they form a sheet on the lower face of the disc or umbrella, which in living specimens is repeatedly opening and closing ; they are continued into the tentacles, and when a velum is present they are largely developed in 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 Bell, F. J. (Francis Jeffrey), 1855-1924. London, Cassell
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