but so are the activities of some of the lowest organisms always recognised as plants-many of the Algæ, especially in their younger stages and reproductive parts, together with such curious plants of prey as Venus's fly-trap and its allies -lately referred to. We do not, indeed, yet positively advocate, though we regard with favour, such a mode of dividing the two component groups which together constitute animated nature; but we confess that we see no possible manner in which these two predominently diverse groups of organisms can be divided, if the whole mass of living creatures which we have seen to be so sharply and distinctly separated off from the non-living world are to be completely, sharply, and distinctly separated, one from the other. Thus, we venture to think, may at present best be answered the two questions with which we set out: (1) What animals and plants are, as contrasted with substances which are neither the one nor the other; and (2) How animals and plants stand towards each other; the answers to which constitute the only reply we know of to the fundamental question we have taken as the title of this paper: What are Animals and Plants?' WEISMANN'S THEORIES-THE BEGINNING AND END OF LIFE. Essays upon Heredity and kindred Biological Problems. By Dr. AUGUST WEISMANN. The Clarendon Press, Oxford, 1889. ONE NE noteworthy characteristic of the latter half of the present century has been the increasing interest taken by the general public in the deeper problems which underlie the natural history of living organisms. At its commencement, the veteran anatomist, Sir Richard Owen, facile princeps of his class, had drawn the attention of many thoughtful minds to questions of biology. He had done so by his skilful restoration of the extinct gigantic birds of New Zealand; his elaborate monographs on the man-like apesespecially the gorilla-and his fascinating theories concerning the archetypal principles of our own bodily structure, and the essential nature of the processes of generation and repair. We recollect a brilliant lecture given at the College of Surgeons to a distinguished audience-whereof one of the most interested was the then Bishop of Oxford, Dr. Wilberforce wherein were expounded certain far-reaching suggestions concerning the then little known lucina sine concubitu -a process termed Parthenogenesis by the learned Hunterian Professor of that day. But however industriously and well Professor Owen may have prepared the way for him who was to follow, it was Charles Darwin who first compelled attention to biology by the efforts he called forth from opponents, as well as by the admiration he excited amongst his followers and disciples. The interest thus forcibly aroused has never been allowed to drop, and it has been recently intensified by the writings of Professor Weismann of Freiburg, upon whom the mantle of Darwin is declared to have fallen by not a few admirers. Strange to say, the subject about which the Freiburg Professor has aroused men's minds of late is mainly the very same as that about which our own Hunterian Professor discoursed so learnedly some forty years ago. A great injustice has been unwittingly committed by those amongst us who, while lauding or criticising Professor Weismann, have failed to make any reference to the work of their aged and illustrious copatriot, who in many respects actually anticipated the ideas of the Freiburg Professor himself. The theories of Professor Weismann, which are now the subject of such earnest discussion amongst our leading men of science, deal especially with what concerns both the beginning and the end of life. Although they do not mainly refer to human life and death, yet the progress of science is continually making more and more evident the close relationship which exists between our own life and the lives of our humbler fellow-creatures-even the very humblest of them. Attention has also become increasingly concentrated upon the processes by which each individual animal or plant is developed from its germ. To this study was devoted the brilliant but far too brief career of the lamented Francis Balfour, of whom it is difficult to say whether he was more esteemed for his scientific knowledge or beloved for his most attractive personal qualities. Investigations concerning development and reproduction have been found to be exceptionally profitable scientifically, so that more varied lines of inquiry have converged upon that mystery of mysteries. 1 See his work on Parthenogenesis. Van Voorst, 1848. VOL. II. 2 B The position which the minds of men interested in the study of living things has thus taken up in our own time, is more or less a return to that mental attitude which marked the earliest days of scientific investigation whereof we have any knowledge. A very large part of Aristotle's biological treatises were directed to this subject, and wonderful indeed are those five books, when studied in the light of our most modern theories. Not of course that such questions were not debated at a yet earlier period. Indeed, a passage in the second chapter of his second book shows that certain very modern theories were rife amongst his predecessors. These he refuted as he refuted Ionian materialism, and his influence for centuries preserved the world from errors of this kind. Owing to this, certain rational ideas about development were retained throughout the Middle Ages-ideas from which the microscopists of the last century went strangely astray. Every one is now familiar with the word 'Evolution,' but during the controversies of the seventeenth and eighteenth centuries it was employed in a very different sense from that in which we now use it. The theory then in fashion was that of 'preformation,' according to which the embryo was a perfect miniature of the adult, its development being a mere process of growth, and the unfolding of what already actually existed. Such were the views of Swammerdam, Vallisneri, Boerhaave, Malpighi, and other celebrated observers. But the same arguments which led to such a belief as regards the individual, logically compelled its supporters to maintain that all the individuals destined to arise in the course of ages also existed 'preformed in miniature'-such preformed germs existing one within the other in ever-diminishing proportions. This was the celebrated theory of 'emboîtement' which, for speculative reasons, received the patronage of Leibnitz and Malebranche. On the other side, our own immortal Harvey (1615) followed the teaching of Aristotle, according to which there took place a gradual formation of what previously had no actual existence but only a potential one. This view, known in modern times as Epigenesis, was strongly reinforced (in 1759) by the careful observations of Caspar Friedrich Wolff; but his efforts remained without effect for two generationsso firmly had the strange theory of 'preformation' become rooted in men's minds. It was deliberately adopted by the great physiologist Haller, was adhered to by Buffon and Bonnet, and not positively rejected even by Cuvier himself. Yet now it is upheld by no one, and the views of Aristotle, Harvey, and Wolff have obtained universal, unhesitating acceptance. Another dispute was independently carried on concerning the predominant effect of paternal or maternal influences. From the most ancient times predominant influence was ascribed to the former, the maternal organisin being regarded merely as an agent for nutrition. Ancient Indian teaching was but echoed by Eschylus1 in the words : Οὐκ ἔστι μήτηρ ἡ κεκλημένου τέκνου Τοκεὺς, τροφὸς δὲ κύματος νεοσπόρου 'The bearer of the so-called offspring is not the mother of it, but only the nurse of the newly-conceived foetus. It is the male who is the author of its being.' Modern supporters of this view came to be known as Animalculists, their opponents being the Ovists. Both notions have now passed, along with 'preformationism,' into the limbo of discarded hypotheses, while the views of Aris 1 Eumenid., 658. 2 After the discovery by Leeuwenhoek and others of seminal particles which he considered to be animalcules. If the reader will refer to a German translation of Vallisneri by Berger, Erzeugung der Menschen und Thiere, he will see marvellous illustrations of the extent to which a prejudiced imagination may mislead an observer. |