fathers, cannot fail to be speedily rewarded by the discovery of truth? Nevertheless, so long as this noise of conflict is in the Senate, we cannot wonder if the people are perplexed. Therefore, in conclusion, I may ask it to be remembered exactly what are the questions--and the only questions--which still divide the parties. Having unanimously agreed that organic evolution is a fact and that natural selection is a cause, or a factor in the process, the primary question in debate is whether natural selection is the only cause, or whether it has been assisted by the co-operation of other causes. The school of Weismann maintain that it is the only cause; and therefore deem it worse than useless to search for further causes. With this doctrine Wallace in effect agrees, excepting as regards the particular case of the human mind. The school of Darwin, on the other hand--to which I myself claim to belong--believe that natural selection has been to a considerable extent supplemented by other factors; and, therefore, although we further believe that it has been the "main" factor, we agree with Darwin himself in strongly reprobating all attempts to bar _a priori_ the progress of scientific investigation touching what, if any, these other factors may be. Lastly, there are several more or less struggling schools, chiefly composed of individual members who agree with each other only to the extent of holding that the causal agency of natural selection is not so great as Darwin supposed. The Duke of Argyll, Mr. Mivart and Mr. Geddes may be named in this connexion; together with the self-styled neo-Lamarckians, who seek to magnify the Lamarckian principles at the expense of the distinctively Darwinian. This primary difference of opinion leads deductively to certain secondary differences. For if a man starts with the premiss that natural selection must necessarily be the "exclusive" cause of organic evolution, he is likely to draw conclusions which another man would not draw who starts with the premiss that natural selection is but the "main" cause. Of these subordinate differences the most important are those which relate to the possible transmission of acquired characters, to the necessary (or only general) utility of specific characters, and to the problem touching the inter-sterility of allied species. But we may well hope that before another ten years shall have passed, even these still outstanding questions will have been finally settled; and thus that within the limits of an ordinary lifetime the theory of organic evolution will have been founded and completed in all its parts, to stand for ever in the world of men as at once the greatest achievement in the history of science, and the most splendid monument of the nineteenth century.