The sum of the matter is that natural selec tion (co ) is the dominant factor, that use and disuse of parts and the action of the en vironment count for nothing, or, at the most, for but a little. (See USE AND Disuse). Here and there Weismann makes concessions as to doe modifying influences of body cells on the rerm-a-ells, and as to the ultimate origin of hereditary individual differences in the direct action of surroundings, which are a partial sur render of his main contention as to the Isola two of the germ-plasm. It is not easy to recon cile the theory of an insulated germ-plasm with the ceaseless manufacture, secretion and expul sion of germ-cells, the materials of which are derived from the materials nourishing the en tire organism; nor with the subtle influence of the nervous system on the reproductive organs.
Perhaps the most serious difficulty in \\ cis mina's theory is in the reconciliation of psy chological evolution with the continuity of the germ-plasm. For the researches of Spencer, Balfour and others have demonstrated that the nervous system had its origin in modifications of the primitive skin due to the direct action of the ens ironment. Be this as it may, the wide
reaching sociological significance of the doctrine of heredity — which may be regarded as the physical correlate of determinism—gives an importance to the labors of Weismann that cannot be overrated, and makes urgent the rec ord of extended observations on the lines al ready laid down by Galion.
Bibliography.— Haeckel, (Generelle Mor phologic' (kW)); I)arwin, 'Variation Under Domestication' (1868); Brooks, 'The Law of Heredity' (1883); Virchow, 'Descendenz stud Pathologic' (Virchow's Archiv, viii, 1886); Eimer, 'Die Entstchung der Arten' (18M); Gahm', 'Natural Inheritance' (1889); Ro manes, 'An Examination of \‘'eistuannisne 12f/3 ) ; Spencer, 'A Rejoinder to Professor riasnann' i1894); Hertwig. (The Biological Problem of To-day' (1894). For critiques of Weismann. consult Eimer, Virchow, op. cit.; Spencer, 'Factors of Organic Evolution' 11/016) ; MeKendrick. 'General Physiology' (IMO and the files of Nature.