The Cell Theory.For a general and historical account of the cell theory see CYTOLOGY.
The cell theory so far as it relates to plants was established by Schleiden in 1838.
But it was only after Darwin that the cell-theory of Schwann was extended to the embryology of the animal kingdom generally, and that the knowledge of the development of an animal became a knowledge of the way in which the millions of cells of which its body is composed take their origin by fission from a smaller number of cells, and these at last from the single egg-cell.
And this demonstration has been completed by the final establishment of the cell theory (see Cytology), which involves the admission of a primitive conformity, not only of all the elementary structures in animals and plants respectively, but of those in the one of these great divisions of living things with those in the other.