General principles of zoology . \ FIG. 29.—Acinous salivary gland of Orthezia cataf> (after List) ; in some acini thenuclei and boundaries of the cells are shown. the secretion of the former must be expelled from the body,so also the sexual cells form elements which are no longer. FIG. 30. —Germinal epithelium of a medusa, ek, ectoderm ; en, entoderm ; o, egg; e, epithelium. a part of the organism, and must reach the exterior in order-to perform their function. Just as the gland-cells areusually scattered among ordinary epithelial cells, so thesexual cells, almost without exception,
General principles of zoology . \ FIG. 29.—Acinous salivary gland of Orthezia cataf> (after List) ; in some acini thenuclei and boundaries of the cells are shown. the secretion of the former must be expelled from the body,so also the sexual cells form elements which are no longer. FIG. 30. —Germinal epithelium of a medusa, ek, ectoderm ; en, entoderm ; o, egg; e, epithelium. a part of the organism, and must reach the exterior in order-to perform their function. Just as the gland-cells areusually scattered among ordinary epithelial cells, so thesexual cells, almost without exception, lie embedded inepithelium ; it may be in the epithelium of the skin (Fig. 30)of the gut, of the body-cavity, or of parts separated fromthis (Fig. 31). This connection of the sexual cells with. GENERAL HISTOLOGY. 95 the epithelium has a still wider basis in the fact that manyorganisms, and particularly organisms of low structure, con-sist exclusively of epithelia and therefore must necessarilydevelop their sexual products in epithelium. In otherwords, sexual and epithelial cells are the oldest elements of
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1896
