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Download or read book The Annals and Magazine of Natural History, Vol. 11 written by and published by . This book was released on 2015-07-26 with total page 494 pages. Available in PDF, EPUB and Kindle. Book excerpt: Excerpt from The Annals and Magazine of Natural History, Vol. 11: Including Zoology, Botany, and Geology The Polype. - The polype may be described as flask-shaped; it bears towards its base a zone of about thirty-two long and imperfectly contractile tentacula arranged in a single series, while at a considerable interval in front of this zone, and a little behind the oral extremity, is a brush-like group of about eighty very contractile tentacula, much smaller and finer than the posterior, and arranged in six or seven closely placed alternate series. Immediately within the zone of posterior tentacula are the branched stalks of the gonophores; their axis is occupied by a continuous tube, which communicates freely with the cavity of the polype, and they carry the gonophores in clusters upon the extremities of the branches. They are usually from fifteen to twenty in number, arranged in two alternate series. The gonophores will be afterwards described. When a longitudinal section is made through the polype from the mouth to the stem, it will be seen that the body, as far back as the zone of posterior tentacula, presents a continuous cavity, with the endodermal lining of the narrow anterior portion thrown into prominent rugae, and with the floor of the cavity projecting as a broad conical elevation into the wide posterior portion. This conical projection consists of a very much vacuolated endoderm; and the same vacuolated structure is continued backwards as far as the origin of the stem, giving to the whole of the posterior part of the polype the appearance of being filled with the vacuolated tissue, and destitute of any distinct cavity. A careful examination, however, will show that this vacuolated mass is perforated in its axis by a tubular prolongation of the cavity of the polype, though, in consequence of temporary obliteration by the approximation of its walls, this continuation of the polypecavity is usually very difficult to detect. It is continued to the summit of the stem, and then, becoming somewhat wider, receives the longitudinal canals of the stem, to be presently described. The posterior tentacula are destitute of any trace of a cavity, and consist of a simple prolongation of the vacuolated endoderm of the body, surrounded by a layer of ectoderm, the endoderm becoming somewhat closer in texture as it enters the tentacula. The anterior tentacula seem to admit the cavity of the polype for a short distance into their interior; but their tube soon becomes obliterated by the vacuolation of their endoderm, which assumes the usual septate appearance. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works."