. Elements of comparative anatomy. Anatomy, Comparative. Fig. 37. 1 Cell with .1 siliceous spicule of Spougilla. 2 Ves- icle with an amphi- disc of Spougilla (after N. Lieber- kiihn). (Fig. 37, 2). The siliceous spicules are ofteu greatly elongated, and form excessively delicate skeletons (Euplectella), or they form bulky structures which project as tufts of fila- ments far beyond the body (Hyalonema). Lastly, in the Fibrospongia?, the skeleton of the body is formed by fibres united into a network, which consist of a substance allied to chitin. In the Acalephas also the deposition of in- organ
. Elements of comparative anatomy. Anatomy, Comparative. Fig. 37. 1 Cell with .1 siliceous spicule of Spougilla. 2 Ves- icle with an amphi- disc of Spougilla (after N. Lieber- kiihn). (Fig. 37, 2). The siliceous spicules are ofteu greatly elongated, and form excessively delicate skeletons (Euplectella), or they form bulky structures which project as tufts of fila- ments far beyond the body (Hyalonema). Lastly, in the Fibrospongia?, the skeleton of the body is formed by fibres united into a network, which consist of a substance allied to chitin. In the Acalephas also the deposition of in- organic substances in the mesoderm leads to the formation of various kinds of skeletons. In the Anthozoa they generally have the form of colonies, and the hard substance is almost always formed of calcareous salts. These give rise to deposits (Fig. 45) of definite form (Fig. 38), which are scattered in the soft parts of the body; or to connected masses, which vary in form according to their mode of development. The calcareous bodies (spicula) always lie in the connective-tissue of the parenchyma, and are very varied in form. They have an organic basis, which retains the form of the spicula after the lime is removed. The connected skeletal parts are formed either by the union of spicula, which are connected to- gether by a hard organic substance, as in Corallium, or by the direct cal- cification of a secreted horny sub- stance, which lies in the axes of the ccenenchyma, and does not possess spicula. When the organic sub- stances predominate the skeleton is horny, as it is in the Gor- gonidre and Antipathidrc. These axial skeletons are sometimes limited to the trunk of the colony, as in the Pennatulida3, where they lie in the shaft of the stock, or they may be continued into all the branches of the stock. There is another form of skeleton, which resembles the axial; it is formed by the gradual calcification of the parenchyma of the body, in which process spicula sometimes take part. I
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Keywords: ., bookcentury1800, bookdecade1870, booksubjectanatomycomparative
