Page:The Effect of External Influences upon Development.djvu/19

Rh He assumed that the histological adaptations might arise by means of intra-selection alone, imagining that its results in a certain individual could be transmitted to the offspring, and thus gradually increase from one generation to another. He even emphasized this particular point, justly conceiving that such finely elaborated adaptations could not have arisen in one lifetime, but must rather have appeared in the course of generations; and he saw no other way in which this could be accomplished except by the transmission of acquired characters.

But there is another way out of the difficulty, and if I am not very much mistaken, Roux himself would now be inclined to regard it as the right one. It is not the particular adaptive structures themselves that are transmitted, but only the quality of the material from which intra-selection forms these structures anew in every individual life. Peculiarities of biophors and cells are transmitted, and these may become more and more favourable and adaptive in the course of generations if they are subject to natural selection. Thus in the course of generations the sensitiveness to tension and pressure has increased in certain of the primary cells of the bones, and it is this sensitiveness which now in every individual life gives opportunity for the processes of intra—selection. It is not the particular spongy plates which are transmitted, but a cell-mass, that from the germ onwards so reacts to tension and pressure that the spongy structure necessarily results. The case is quite similar to that of plants, in which geotropic sensitiveness makes the root grow