Animal breeding / by Laurence M. Winters.

  • Winter, Laurence Merriam, 1891-
Date:
1925
Catalogue details

Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Animal breeding / by Laurence M. Winters. Source: Wellcome Collection.

    30/328 (page 16)
    16 THE BIOLOGICAL FOUNDATION—THE CELL by differentiation, so that one part is distinctly different from another. 5. As growth proceeds bits of this bulk are thrown off, each of which constitutes a new individual capable of independent existence,—reproduction. 6. The new individual is substantially, but never exactly, like the one from which it arose, and here Ue the chief mysteries of breeding. In reproduction there are no duphcates. The vital characteristics of protoplasm are its capa¬ bility of movement, irritability and power of assimilation and of reproduction. Protoplasm is composed of three intrinsic materials, viz., reticulum, cell-sap, and microsomes. The reticulum forms a network which is filled with the cell-sap, and the micro¬ somes, which are minute granules, are distributed along the lines of the network. 8. The Nucleus.—The nucleus is a body enclosed in the cytoplasm. It is the center of the cell's constructive activ¬ ities. In a cell devoid of a nucleus, the only possible activ¬ ities are destructive ones, decomposition. The nucleus is the regulating center of cell activity; it is the principal factor in growth, development, and the transmission of precise attributes from parent to daughter cell or generation to generation. Growth results from cell division, and the nucleus apparently gives the necessary impetus for cell division; for it is essential, in cell division, that a portion of the nuclear material of the parent cell pass into the new cell. The new cell in turn divides and thus growth goes on. The typical nucleus is oval; but it may be rod-shaped, bent like a horseshoe, tree-shaped, or in the form of a rosary. It exhibits two distinct phases: the vegetative or resting stage, and the active stage during which cell division and reproduction occur, 9. The Nuclear Substance.—A typical nucleus during the vegetative stage is constructed as described below: