In retaliation for the destructive criticism of natural selection, the Neo-Darwinians have proceeded to pulverize the Lamarckian tenet concerning the inheritability of acquired adaptations. Weismann, having laid down his classic distinction between the _soma_ (comprising the vegetative or tissue cells in contact with the environment) and the _germ_ (_i.e._ the sequestered reproductive cells or gametes, which are sheltered from environmental vicissitudes), showed that the Lamarckian assumption that a change in the somatic cells (which constitute the organism of the individual) is registered in the germ cells (which constitute the vehicle of racial inheritance), is supported neither by _a priori_ probability nor by any facts of observation. Germ cells give rise by division to somatic or tissue cells, but the converse is not true; for, once a cell has become differentiated and specialized into a tissue cell, it can never again give rise by division to germ cells, but only to other tissue cells of its own kind. Hence the possibility of a change in the tissue being transmitted to the germ has no antecedent probability in its favor. Neither is it grounded on the facts of observation. Bodily mutilations of the parent are not transmitted to the offspring. The child of a blacksmith is not born with a more developed right arm than that of a tailor’s child. When the ovaries from a white rabbit are grafted into a black rabbit, whose own ovaries have been previously removed, the latter, if mated to a white male, will produce spotlessly white young. Hence the offspring inherit the characters of the germ track of the white female, whence the ovaries were derived, without being influenced in the least by the pigmented somatic cells of the nurse-body (_i.e._ the black female), into which the ovaries were grafted. Kammerer’s experiments, in which young salamanders were found to exhibit at birth the coloration, which their parents had acquired through the action of sunlight, fail to convince, because, in this case, the bodies of the parents are not sufficiently impervious to light to preclude its direct action upon the gametes while in the reproductive organs of the parents. Hence we cannot be sure but that the coloration of the offspring derived from these gametes is due to the direct agency of sunlight rather than to the intermediate influence of the modified somatic cells upon the germ plasm.