Page:George Archdall Reid 1896 The present evolution of man.djvu/71

Rh organism, when it is no longer directly affected by those changes, to proliferate into an individual who has the same kind of variation as the acquired variation in the parent? Why should not the result be enlarged leg muscles or an enlarged brain or liver? Is it conceivable, if a man takes exercise in such a manner as to enlarge the muscles of his legs, that the nutritive fluids will thereby be so differently changed from what they would be if he took such exercise as would enlarge his arm muscles, as will confer on the germ such a constitution as will cause it to proliferate into an organism with enlarged leg muscles rather than enlarged arm muscles? I think we may dismiss this hypothesis also as unbelievable.

The second of these theories is weighted with the authority of a great and honoured name. Darwin, in striving to account for the fact that complex and heterogeneous multicellular organisms are able to reproduce their like by means of germ cells, supposed that each cell of the multicellular organism sends off portions, which he called gemmules, of itself, which gemmules, entering into the substance of the germ cell, so affect its constitution as to cause it, when fertilized, to proliferate into an organism like to that from which it was derived. Since Darwin held that acquired variations are transmissible, this, his theory of "Pangenesis," must include the corollary that when any part of the organism, for instance the arm muscles, varies in such a manner as to increase the number of its cells, the additional cells send off additional gemmules to each of the germ cells, whereas if it varies in such a manner as to decrease the number of its cells, a number of gemmules corresponding to the decrease are in some way withdrawn from each of the germ cells.

Now the germ cells of many animals, as for instance of a man, are numbered by millions, the other cells, the