But Professor Weismann does not like such cases, and admits that he cannot explain the facts in connection with the climatic varieties of certain butterflies, except “by supposing the passive acquisition of characters produced by the direct influence of climate.”

Nevertheless, in his next paragraph but one he calls such cases “doubtful,” and proposes that for the moment they should be left aside.  He accordingly leaves them, but I have not yet found what other moment he considered auspicious for returning to them.  He tells us that “new experiments will be necessary, and that he has himself already begun to undertake them.”  Perhaps he will give us the results of these experiments in some future book—­for that they will prove satisfactory to him can hardly, I think, be doubted.  He writes:—­

“Leaving on one side, for the moment, these doubtful and insufficiently investigated cases, we may still maintain that the assumption that changes induced by external conditions in the organism as a whole are communicated to the germ-cells after the manner indicated in Darwin’s hypothesis of pangenesis, is wholly unnecessary for the explanation of these phenomena.  Still we cannot exclude the possibility of such a transmission occasionally occurring, for even if the greater part of the effects must be attributable to natural selection, there might be a smaller part in certain cases which depends on this exceptional factor.”

I repeatedly tried to understand Mr. Darwin’s theory of pangenesis, and so often failed that I long since gave the matter up in despair.  I did so with the less unwillingness because I saw that no one else appeared to understand the theory, and that even Mr. Darwin’s warmest adherents regarded it with disfavour.  If Mr. Darwin means that every cell of the body throws off minute particles that find their way to the germ-cells, and hence into the new embryo, this is indeed difficult of comprehension and belief.  If he means that the rhythms or vibrations that go on ceaselessly in every cell of the body communicate themselves with greater or less accuracy or perturbation, as the case may be, to the cells that go to form offspring, and that since the characteristics of matter are determined by vibrations, in communicating vibrations they in effect communicate matter, according to the view put forward in the last chapter of my book Luck or Cunning, then we can better understand it.  I have nothing, however, to do with Mr. Darwin’s theory of pangenesis beyond avoiding the pretence that I understand either the theory itself or what Professor Weismann says about it; all I am concerned with is Professor Weismann’s admission, made immediately afterwards, that the somatic cells may, and perhaps sometimes do, impart characteristics to the germ-cells.