. Elements of zoology, or, Natural history of animals / ed. by Reese. Zoology. HYPR01DA THE SRRTULARIDJB. f>07 or polype, opens at its lower part by a throat-like aperture, which is capable of being enlarged or contracted, or entirely closed. The (ubularia is a marine animal, and the tube, which often at- tains the length of from eight to twelve inches, is attached at its base to rocks. A very curious circulation of fluid takes place within it, the current passing up one side and down the other; this appears independent of any movement of the polype at its summit. In some species, the
. Elements of zoology, or, Natural history of animals / ed. by Reese. Zoology. HYPR01DA THE SRRTULARIDJB. f>07 or polype, opens at its lower part by a throat-like aperture, which is capable of being enlarged or contracted, or entirely closed. The (ubularia is a marine animal, and the tube, which often at- tains the length of from eight to twelve inches, is attached at its base to rocks. A very curious circulation of fluid takes place within it, the current passing up one side and down the other; this appears independent of any movement of the polype at its summit. In some species, the tubes send ofFbuds or branches, and the polypes do not appear at their extremities until they are fully formed, which shows that the horny tube, and the contained membrane, are themselves endowed with independent vitality. 898. In another group we find the polype itself enclosed in a horny cell of similar character, from which its body can be pro- truded in search of food. This is the case in the family of Sek- itrLABiDJB, so named from the Scrtidaria, which is its most com- mon and characteristic genus. In these compound structures, the cells are con- nected by stems and branches, in the same manner as the buds of a plant; and through the base of each cell there is a canal, lined, as in the Tubularia, by an extension of the lining membrane of the polype, and uniting with the channels which pass through the whole structure. Thus all the polypes are brought into connection with each other, and with the general mass or poly-Portion of Sertularia: a a, pary; and the circulation of fluid, which polype cells with polypes; may be observed to take place in the b 6> ovanal veSicles' stem and branches, independently of any mechanical action of the polypes, proves the vitality of the former. Indeed, we may rather say that the polype is an extension of the lining membrane of the stem, than the latter a prolongation of the sto- mach of the polype; for the stem and cells upon it are form
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