. Biologie der Tiere. Zoologie; Biologie. anderen Fällen die Sekretion der Zerstörung der gesamten Zelle, in der Sie Ihre Inhalt gießt die Sekretion in Form beinhaltet; Beispiele sind Milch und sebaceous Drüsen, Öl, Drüsen. Wenn Epithelzellen eine Änderung, welche Macht sie hart, die Substanz gebildet wird, Horn, welches chemisch eine Substanz namens Keratin. Auf diese Weise echte Hörner, Klauen, Nägel und Schildpatt entwickelt. Im Falle der Zähne und einige Größenordnungen von Wirbeltieren, jedoch, Emaille kann der Stoff hergestellt. In einigen Fällen Epithelien produzieren eine harte Abdeckung durch die aushärtung eines

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. Animal biology. Zoology; Biology. other cases the secretion involves the destruction of the whole cell, which pours out its contents to form the secretion; examples are milk glands and sebaceous, or oil, glands. When epithelial cells undergo a change which makes them hard, the substance formed is horn, which chemically is a substance called keratin. In this fashion true horns, claws, nails, and tortoise shell are developed. In the case of teeth and some scales of vertebrates, however, enamel may be the substance produced. In some cases epithelia produce a hard covering by the hardening of a secretion; an example of such a hard covering is the cuticula of the bodies of insects, which contains chitin. 122. Supporting and Connective Tissues.—These tissues are found in all parts of the body and differ from other tissues in the fact that the character of the tissue depends not so much upon the cells which it contains as upon nonliving intercellular materials formed by secretion from these cells. Examples of such materials are fibers, bone, and cartilage. Most of the embryonic connective tissue appears in the form of a network of branched cells and is known as mesenchyme. A prominent function of these tissues is support, either of the body as a whole or of some particular part. Among supporting tissues having this func- tion are fibrous tissues, which are characterized by JheUa^ceTii?" A^ cdis bundles of fibers or single fibers between the cells, of such a gland as the White, nonelastic fibers are usually collected in ifeZLt^'lZZn bundles, while yellow, elastic fibers are, in most cases, granules accumulated single and, sincc they branch and run together, tend idiltnfto ttmt to form a network. The fibrous tissues also serve or cavity, of the gland, to bind parts together and to hold them in place. tt'TntStilTe ;f;'r- Another type of supporting tissue is cartUage, in tebrate showing the which the space between the cells is occupied by a accumulation of mucus g^bg^

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• bookcentury1900
• booksubjectzoology
• buchrolle
• buchsubjektbiologie