The Principles of Biology, Volume 1 · Herbert Spencer
CELL-LIFE AND CELL-MULTIPLICATION.
Maturation of the ovum having been completed, entrance of the spermatozoon, sometimes through the limiting membrane and sometimes through a micropyle or opening in it, takes place. This instantly initiates a series of complicated changes: not many seconds passing before there begins the formation of an aster around one end of the spermatozoon-head. The growth of this aster, apparently by linear rangings of the granules composing the reticulum of the germ-cell, progresses rapidly; while the whole structure hence arising moves inward. Soon there takes place the fusion of this sperm-nucleus with the germ-nucleus to form the cleavage-nucleus, which, after a pause, begins to divide and subdivide in the same manner as cells at large: so presently forming a cluster of cells out of which arise the layers originating the embyro. The details of this process do not concern us. It suffices to indicate thus briefly its general nature. And now ending thus the account of genesis under its histological aspect, we pass to the account of genesis under its wider and more significant aspects.
Ideas discussed in this chapter
Text from Project Gutenberg, public domain in the United States.