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In order to explain the developing organism Weismann assumes that each of its organs or parts, or “independent regions,” is represented in the germ-plasm by a determinant, upon the fate of which the development of the future determinate depends. It is thought of as a very minute corpuscle of living matter. Thus there are determinants of hairs and scales, pieces of skin, pits, marks, &c.
What was said there applies to women as to men. That is true so far as the individual is concerned and it is also true that, so far as the race is concerned, the germ-plasm or germ-cells in both sexes alike may be injured by the continued consumption of large quantities of alcohol.
The difference between Professor Weismann and, we will say, Heringians consists in the fact that the first maintains the new germ-plasm when on the point of repeating its developmental processes to take practically no cognisance of anything that has happened to it since the last occasion on which it developed itself; while the latter maintain that offspring takes much the same kind of account of what has happened to it in the persons of its parents since the last occasion on which it developed itself, as people in ordinary life take of things that happen to them.
In order to explain the mystery of heredity, Weismann long ago elaborated, in his germ-plasm theory, the doctrine that the developing individual is materially preformed, or rather predetermined in the “idants” and “ids” of the germ-cell.
The protoplasm must differ in chemical, or molecular, or other structure in the two cases, and we distinguish the germ-plasm of the germ-cells, resembling in certain respects Nägeli's idioplasm, from somatoplasm, which performs most of the functions of the cell. The somatoplasm arises from, and hence must be regarded as a modification of, the germ-plasm.
The fundamental question connected with the theory of heredity is: How can a single cell of the body contain within itself all the hereditary tendencies of the hypothesis of the continuity of the germ-plasm gives an identical starting-point to each successive generation, and thus explains how it is that an identical product arises from all of them.
But the very constitution of the germ-plasm and its relation to the body absolutely forbids the transmission of acquired somatic characteristics and of the special effects of use and disuse. Muscular activity promotes general health, and might thus conduce to better-nourished germ-cells and to more vigorous and therefore athletic descendants.
The germ-plasm can increase indefinitely in the lapse of generations, increase of the somatoplasm is limited. When a new individual develops, a certain portion of the germ-plasm of the egg is set aside and remains unchanged in structure. This, increasing in quantity, forms the reproductive elements for the next generation.
On the contrary, we have to accept, at least in general and as substantially revealing to us the true nature of the individual, the doctrine of the "continuity of the germ-plasm," which teaches that the race proper is a potentially immortal sequence of living germ-cells, from which at intervals there are developed bodies or individuals, the business and raison d'être of which, whatever such individuals as ourselves may come to suppose, is primarily to provide a shelter for the germ-plasm, and nourishment and air, until such time as it shall produce another individual for itself, to serve the same function.
It is well known that, on the theory of the "continuity of the germ-plasm," maintained by Weismann, the sexual elements of the generating organism pass on their properties directly to the sexual elements of the organism engendered.
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