. Text book of zoology. Zoology. Cells and Tissues. 9 central cavity, wherein is contained the substance separated from the protoplasm {, mucus), and this escapes to the exterior through an aperture. Secreting cells commonly consist of a long thin neck, wedged between the adjacent epithelial cells, and a wide sac-shaped inner part, lying in the deeper tissues. All secreting cells derived from the general epithelium are called glandular cells, for any part of the animal body which forms a secretion is considered to be a gland. Sometimes glandular activity is distributed over a large, contin
. Text book of zoology. Zoology. Cells and Tissues. 9 central cavity, wherein is contained the substance separated from the protoplasm {, mucus), and this escapes to the exterior through an aperture. Secreting cells commonly consist of a long thin neck, wedged between the adjacent epithelial cells, and a wide sac-shaped inner part, lying in the deeper tissues. All secreting cells derived from the general epithelium are called glandular cells, for any part of the animal body which forms a secretion is considered to be a gland. Sometimes glandular activity is distributed over a large, continuous area of the epithelium, which is usually invaginated into the subjacent connective tissue; such are true glands. In its simplest form the gland is a flat patch of cells, a pit, a small sac, or a longer tube; but the tube itself may form evaginationSj and these on their part may possess branches, and so 1 nm^iiSMxn. 3 4 Fig. 9. Diagrams of different true glands. The secreting cells are dotted. 1 The ' simplest form; the secreting cells are not invaginated. 2—5 Different kinds of simple glands. 6 Branched tabular gland. 7 Eaoemose gland.—Orig. on; SO that a compound gland is made up of a complex system of canals (the walls of which consist of a single layer of epithelium), held together and supported by connective tissue [see below). In these large glands, the ends of the branches only secrete, whilst the rest of the system serves as a reservoir and as a means of exit. Such a distinction into secreting portion and duct, may be noticed even in very simple glands. Sometimes the ends of the canals exhibit a rounded enlargement, when the gland is called racemose, to distinguish it from the tubular gland, which is without this expansion. Tor the development of sensoiT' epithelium, see " ; 2. Skeletal tissue is characterized by the great prominence of the intercellular substance. In an early stage of develop- ment it consists, like epithelia, of cells on
Size: 1928px × 1296px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectzoology, bookyear1896
