All that is really meant by "immortality" in a germplasm is continuity. That is, while an individual may consist of a colony of millions of cells, all of these spring from one cell and it a germ cell--the fertilized ovum. This first divides to form a new group of germ cells, which are within the embryo or new body when it begins to develop, and so on through indefinite generations. Thus the germ cells in an individual living to-day are the lineal descendants, by simple division, of the germ cells in his ancestors as many generations, or thousands of generations, ago as we care to imagine. All the complicated body specializations and sex phenomena may be regarded as super-imposed upon or grouped around this succession of germ cells, continuous by simple division. The type of body in each generation depends upon this germplasm, but the germplasm is not supposed to be in any way modified by the body (except, of course, that severe enough accidents might damage it). Thus we resemble our parents only because the germplasm which directs our development is a split-off portion of the same continuous line of germ cells which directed their development, that of their fathers, and so on back. This now universally accepted theory is called the "continuity of the germplasm." It will be seen at once that this seems to preclude any possibility of a child's inheriting from its parents anything which these did not themselves inherit. The bodies of each generation are, so to speak, mere "buds" from the continuous lines of germplasm. If we _develop_ our muscles or our musical talent, this development is of the body and dies with it, though the physical basis or capacity we ourselves inherited is still in the germplasm and is therefore passed along to our children. We may also furnish our children an environment which will stimulate their desire and lend opportunity for similar or greater advancement than our own. This is _social inheritance_, or the product of _environment_--easy to confuse with that of _heredity_ and very difficult to separate, especially in the case of mental traits.