We will be able to understand his theory better from the following quotations, which give his own words. He says: "I have called this substance 'germ-plasm,' and have assumed that it possesses a highly complex structure, conferring upon it the power of developing into a complex organism." ("Heredity," Vol. I, p. 170.) Again he says: "There is, therefore, continuity of the germ-plasm from one generation to another. One might represent the germ-plasm by the metaphor of a long, creeping rootstock from which plants arise at intervals, these latter representing the individuals of successive generations. Hence it follows that the transmission of acquired characters is an impossibility, for if the germ-plasm is not formed anew in each individual, but is derived from that which preceded it, its structure, and, above all, its molecular constitution, cannot depend upon the individual in which it happens to occur, but such an individual only forms, as it were, the nutritive soil at the expense of which the germ-plasm grows, while the latter possessed its characteristic structure from the beginning, viz., before the commencement of growth. But the tendencies of heredity, of which the germ-plasm is the bearer, depend upon this very molecular structure, and hence only those characters can be transmitted through successive generations which have been previously inherited, viz., those characters which were potentially contained in the structure of the germ-plasm. It also follows that those other characters which have been acquired by the influence of special external conditions, during the lifetime of the parent, cannot be transmitted at all." (Vol. I, p. 273.) In conclusion, Weismann writes: "But at all events we have gained this much, that the only facts which appear to directly prove a transmission of acquired characters have been refuted, and that the only firm foundation on which this hypothesis has been hitherto based has been destroyed."(Vol. I, p. 461.) Thus we see how far the theory of heredity has been pushed by the great scientific investigators of the present age. We have no longer any right to believe in the old oft-refuted hypothesis which assumes that each individual organism produces germ-cells afresh again and again and transmits all its powers developed and acquired by the parents; but, on the contrary, we have come to know to-day that parents are nothing but mere channels through which these germ-plasms or germ-cells manifest their peculiar tendencies and powers which existed in them from the very beginning. The main point is that the germs are not created by the parents, but that they existed in previous generations.