In regard to the issue between the Lamarckians and Weismannists--whether changes acquired by the parent are inherited by the young--recent experiments again suggest something of a compromise. Weismann says that the body of the parent is but the case containing the germ-plasm, so that all modifications of the living parent body perish with it, and do not affect the germ, which builds the next generation. Certainly, when we reflect that the 70,000 ova in the human mother's ovary seem to have been all formed in the first year of her life, it is difficult to see how modifications of her muscles or nerves can affect them. Thus we cannot hope to learn anything, either way, by cutting off the tails of cows, and experiments of that kind. But it is acknowledged that certain diseases in the blood, which nourishes the germs, may affect them, and recent experimenters have found that they can reach and affect the germs in the body by other agencies, and so produce inherited modifications in the parent. [*] If this claim is sustained and enlarged, it may be concluded that the greater changes of environment which we find in the geological chronicle may have had a considerable influence of this kind. * See a paper read by Professor Bourne to the Zoological Section of the British Association, 1910. It must be understood that when I speak of Weismannism I do not refer to this whole theory of heredity, which, he acknowledges, has few supporters. The Lamarckian view is represented in Britain by Sir W. Turner and Professor Darwin. In other countries it has a larger proportion of distinguished supporters. On the whole subject see Professor J. A. Thomson's "Heredity" (1909), Dewar and Finn's "Making of Species" (1909--a Mendelian work), and, for essays by the leaders of each school, "Darwinism and Modern Science" (1909). The general issue, however, must remain open. The Lamarckian and Weismannist theories are rival interpretations of past events, and we shall not find it necessary to press either. When the fish comes to live on land, for instance, it develops a bony limb out of its fin. The Lamarckian says that the throwing of the weight of the body on the main stem of the fin strengthens it, as practice strengthens the boxer's arm, and the effect is inherited and increased in each generation, until at last the useless paddle of the fin dies away and the main stem has become a stout, bony column. Weismann says that the individual modification, by use in walking, is not inherited, but those young are favoured which have at birth a variation in the strength of the stem of the fin. As each of these interpretations is, and must remain, purely theoretical, we will be content to tell the facts in such cases. But these brief remarks will enable the reader to understand in what precise sense the facts we record are open to controversy.