Page:Popular Science Monthly Volume 45.djvu/193

Rh tissues through which even biophors can not pass; and Prof. Weismann, in showing that the latter must break out of jail, should also explain how the former are able to break into jail. Taking all these things into account, I am constrained to repeat a former remark, that "if the term 'acquired' is to be any further refined away, then discussion is useless, for it is not a mere dispute about a word that interests us, but the fundamental question whether external conditions do or do not permanently and progressively influence the development of organic beings."

Reverting, then, to the main question as to the influence of external conditions on the germ, I would remind the reader that in his essay on amphimixis, originally published in 1891, Prof. Weismann held that "a belief m the inheritance of acquired characters by the highly differentiated Protozoa, as ivell as by Metazoa, must be opposed," and imagined that "the phyletic modifications of Protozoa arise from the germ-plasm, that is from the idioplasm of the nucleus"; and he further says:

"My earlier views on unicellular organisms as the source of individual differences, in the sense that each change called forth in them by external influences, or by use and disuse, was supposed to be hereditary, must therefore be dismissed to some stage less distant from the origin of life."

He then ascribed all variations above this early stage to amphimixis and sexual reproduction. In the new work he indeed reiterates this view, and says that these processes furnish "an inexhaustible supply of fresh combinations of individual variations which are indispensable to the process of selection." But he now introduces the following important qualification:

"Although the process of amphimixis is an essential condition for the further development of the species, and for its adaptation to new conditions of existence among the higher and more complicated organisms, it is not the primary cause of hereditary variation."

He then proceeds to explain the change that has taken place in his mind, obviously while writing this book, admits that he had overestimated the power of sexual reproduction to modify species, and shows that though the general result might be changed there could be no variation in the determinants themselves, "which alone could gradually lead to a transformation of the species." Not only is amphimixis incapable of modifying the determinants, but it is also, and for the same reason, incapable of increasing the number of kinds, yet on his general theory these