Lectures on the comparative anatomy and physiology of the invertebrate animals : delivered at the Royal College of Surgeons . rmed by the secretion of a simple sac,excavated in the gelatinous and granular parenchyme of the the second class, called Anthozoa, the digestive sac, which, likethe first, throws out the rejectamenta by the same aperture as that which receives thenutriment, is suspendedby a series of verticalfolds of membrane, ina distinct abdominal ca-vity, to the outer parietesof the body. In the) third and highest class,called Bryozottf the ali-mentary canal, which issuspend
Lectures on the comparative anatomy and physiology of the invertebrate animals : delivered at the Royal College of Surgeons . rmed by the secretion of a simple sac,excavated in the gelatinous and granular parenchyme of the the second class, called Anthozoa, the digestive sac, which, likethe first, throws out the rejectamenta by the same aperture as that which receives thenutriment, is suspendedby a series of verticalfolds of membrane, ina distinct abdominal ca-vity, to the outer parietesof the body. In the) third and highest class,called Bryozottf the ali-mentary canal, which issuspended loosely in anabdominal cavity, is pro-vided, as has been alreadystated, with a distinctmouth and anus. It is remarkable thatthe most locomotive of thePolype tribe is at thesame time the type of thelowest organised Hydra\, or commonfresh-water Polype {) consists, when mag-nified even with a mode-rately high power, appa-rently of a granular sub-stance of a greenish orreddish hue, the granules or cells being loosely connected by a semi-fluid matter. The external cells are condensed, and elongated in the. Hydra fusca. * Nat. size. * LXXXIV. p. 82. Dimorphoea of Ehrenberg ; Sertulariens of Miliie Edwards ;Nudihrachiata of Fane; Hydroida of Johnston ; Hydraidce and Sertulariadce ofE. Eorbes. f In Africa et Arabia Hydras studiose fnistra qu£esivi, CXVIL, p. 292. POLYPI. 121 axis of tlie body, so as to form two tegumentary layers : the internalcells are elongated transversely to the axis of the body, and form astratum of villi, projecting into the abdominal cavity: the thickintermediate mass of nucleated cells seems to fulfil the ordinaryfunctions of muscular or contractile tissue. The hydra commonly adheres by a small prehensile disc or rudi-mentary foot {^fig. 60, d\ situated at the extremity of the stem orbody opposite to the mouth. When the little animal would changeits position it slowly bends its body, and, fixing one or more of itstentacula to the supporting
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