the infusorians do, by dividing the one into two or more; never do two or more cells unite to form another cell, or by giving off living portions of their substance unite, themselves maintaining their individual existences, to form in part or whole another cell—a germ cell, for instance. The germ cells are therefore not produced by other co-existing cells, but are co-descendants with the other cells from a common ancestry. Now if among mammals it is true that the cell-descendants of a pair of conjuated germ cells do not conjugate among themselves, nor emit portions of themselves which unite to form other cells, and it certainly is true if we are to judge by what happens among unicellular animals, among whom the behaviour of cells in this respect can best be observed, it is impossible to understand how acquired variations can be transmissible.
To take an example already given: the muscles in the blacksmith's arm are enlarged by exercise, i.e. the muscle cells in the arm, when stimulated by exercise, undergo proliferation and are so multiplied. Now if the blacksmith's child is to inherit his acquired variation, his germ cells, situated far distant from the muscle cells of his arm, and related to them only through a remote cell ancestry, must be so influenced, so structurally altered, as to produce spontaneously in some of their very remote cell-descendants (i.e. in the muscle cells of the child's arm) that modification in point of numbers which exercise temporarily produced in the muscle cells of the blacksmith's arm. Is this possible?
I have heard it contended that the muscle cells telegraph by means of the nerves, or in some other way communicate what practically amounts to an order to the germ cells to structurally modify themselves in the desired way, but of course such a theory is too absurd to be met with anything but derision. It is, scientifically speaking, so utterly ridiculous as to be
