will increase both in size and weight, and will at the same time become more fully competent to discharge its particular work. On the other hand, disuse of a muscle leads, in the first place, to a decreased ability on the part of the organ to perform its proper function. Thus, the muscles of the left hand cannot in ordinary people be used as efficiently as those of the right hand, because they are less often used. If the disuse be prolonged and habitual, the organ diminished in size, and the function may be wholly lost. will become ability to discharge its Thus, man possesses the three muscles which are attached to the external ear, and which enable many of the quadrupeds to move their ears freely; but in him they are extremely reduced in size, and the power of employing them has, from disuse, become almost, or entirely, lost. Finally, if the disuse of an organ be complete, as when external conditions no longer demand its employment, it may become a mere rudiment, absolutely destitute of function. This is the case, for example, with the eyes of certain animals which spend their existence living underground and in total darkness. Lamarck fully recognised the important results which flow from the use or disuse of organs; and it was, therefore, to the effects of habit that he chiefly ascribed the progressive modifications which he believed to have affected the structure of all living beings. He believed that a change in the surrounding conditions would necessarily compel an animal to modify its former habits of life; and that a change in its habits would necessarily entail an increased use of certain organs and a decreased use of others. The organs upon which new and increased demands were made would undergo a proportionate development in size, and would simultaneously become better fitted for their work. At the same time, they might become modified in form, and thus might become better suited for the purposes for which they were required. On the other hand, the organs which were called into action less frequently than they had previously been, would gradually diminish in size, and might ultimately disappear. By a continuance of this process through many successive generations, the whole organisation of an animal might become profoundly modified. This was therefore the process by which, in the main, Lamarck believed that 'species' had been evolved out of other pre-existing forms of life. K THE DOCTRINE OF PROGRESSIVE DEVELOPMENT. 6 BEFORE proceeding to give a sketch of the theory of 'Natural Selection,' as propounded by Charles Darwin, a brief consideration may be fitly given to the celebrated work entitled the 'Vestiges of Creation.' This wellknown treatise was first published in 1844, and the tenth edition appeared in 1853, a sufficient proof of the wide popularity which it enjoyed. Its authorship was never acknowledged during the lifetime of its writer, and it was ascribed to various distinguished persons, with the most varied qualifications for the writing of such a work. Amongst others, Robert Chambers was selected as the author of the 'Vestiges,' and in this instance, as now openly acknowledged, the surmise was correct.* As, however, the work was an anonymous one, the personality of the writer may well * A twelfth edition of the 'Vestiges' was published in 1884 (W. & R. Chambers), containing a preface by Mr Alexander Ireland, in which the facts relating to the authorship are given in detail. be left out of account in the few remarks which will here be made as to its general scope and teaching. The 'Vestiges' not only dealt with the origin of the various forms under which vitality has been manifested in the past, or is exhibited at the present day; but it also took up the much wider and much more inscrutable problem of the origin of life itself. It was therefore more than simply an attempt to explain the origin of 'species.' The work is remarkable for the ability which it displays in the handling of general principles, for the closeness of its reasoning, for the clearness with which fallacies are detected and exposed, for the lucidity of its style, and for the wealth of its suggestions. It is, nevertheless, inadequate for the purpose which the writer proposed to himself as the object of his labours. It is, namely, unmistakably, the work of a writer who had mastered the general facts and principles of zoology and the kindred sciences, but who at the same time was without that minute knowledge of biological science which can be obtained in no other way save by longcontinued and rigidly conducted first-hand investigation into the phenomena presented by living beings. No fact, indeed, stands out more clearly in the whole history of science than the insufficiency of a merely general knowledge for the establishment of generalisations of any kind. Only the worker whose mind is stored with the minutest details of his subject can safely enter upon the task of generalisation. Having premised so much, we may briefly sketch the conclusions which are set forth in the 'Vestiges.' After a general review of the relations of the earth to the solar system, and of other astronomical considerations which bear upon geology, an outline is given of the known facts as to the life-history of the earth, and as to the general succession and progression of organic types in past time. With regard to the purely geological history of the earth, the writer of the 'Vestiges' concludes, with Lyell, that there is nothing in the whole series of operations displayed in inorganic geology, which may not be accounted for by the agency of the ordinary forces of nature.' On the other hand, the past history of the earth is not a mere record of physical changes. 'Mixed up with the geognostic changes, and apparently as a final object connected with the formation of the globe itself, there is another set of phenomena presented in the course of our history-the coming into existence, namely, of a long suite of living things, vegetable and animal, terminating in the families which we still see occupying the surface. The question arises-In what manner has this set of phenomena originated? Can we touch at and rest for a moment on the possibility of plants and animals having likewise been produced in a natural way; thus assigning immediate causes of but one character for everything revealed to our sensual observation; or are we at once to reject this idea, and remain content, either to suppose that creative power here acted in a different way, or to believe, unexaminingly, that the inquiry is one beyond our powers?' In answering this question, the writer of the 'Vestiges' decides unhesitatingly, as every naturalist would at the present day decide, that we cannot consistently accept |