This work is considered by some writers to be the greatest produced by Darwin; but I think we shall be right in accepting his own opinion that such words should be applied to the “Origin.” It is probable, however, that this book stands second in importance in the splendid list of works which have done so much to increase our knowledge of nature and to inspire others to continue the good work. [Sidenote: ON VARIATION.] “The Variation of Animals and Plants under Domestication” opens with a very clearly written account of natural selection; it proceeds to treat of the domestic quadrupeds and birds, describing the differences between the various breeds of each species, and making out as far as possible the history of their development from each other and from the wild stock. Cultivated plants are then treated in the same manner. The first volume concludes with two most important chapters on bud-variation and anomalous modes of reproduction, and on inheritance. The second volume deals with inheritance, crossing, effect of conditions of life, sterility, hybridism, selection by man, causes and laws of variability. Finally, all the main lines are brought to a common centre in the wonderful chapter in which he discloses his “provisional hypothesis of pangenesis.” This is of such interest, and is so characteristic of its author’s power of viewing the most divergent facts from a common standpoint, that it is desirable to give a tolerably full account of it. The following is a brief statement of the various classes of facts which Darwin attempted to connect by his hypothesis. _Reproduction_ is sexual and asexual, and the latter is of various kinds, although their differences are more apparent than real. It may be concluded that gemmation or budding, fission or division, the repair of injuries, the maintenance of each part, and the growth of the embryo “are all essentially the results of one and the same great power.” In parthenogenesis the ovum can develop without fertilisation, and hence the union of germs from different individuals cannot serve as an essential characteristic of sexual, as compared with asexual, generation. Although sexually-produced individuals tend to vary far more than those which are produced asexually, this is not always the case, and the variability, when it occurs, is subject to the same laws. Sexually-produced individuals very generally pass in development from a lower to a higher grade; but this can hardly be said to occur in certain forms, such as Aphis, etc.