Page:Encyclopædia Britannica, Ninth Edition, v. 24.djvu/851

Rh ZOOLOGY 801 in Linnceus, a new type of student made its appearance in such men as John Hunter and other anatomists, who, not satisfied with the superficial observations of the popular &quot;zoologists,&quot; set themselves to work to examine anatomic ally the whole animal kingdom, arid to classify its members by aid of the results of such profound study. From them we pass to the comparative anatomists of the 19th century and the introduction of the microscope as a serious instru ment of accurate observation. The influence of the scientific academies and the spirit in which they worked in the 17th century cannot be better illustrated than by an examination of the early records of the Eoyal Society of London. The spirit which animated the founders and leaders of that society is clearly indicated in its motto &quot;Nullius in verba.&quot; Marvellous narrations were not permitted at the meetings of the society, but solely demonstrative experiments or the exhibition of actual specimens. Definite rules were laid down by the society for its guidance, designed to ensure the collection of solid facts and the testing of statements embodying novel or remarkable observations. Under the influence of the touch stone of strict inquiry set on foot by the Royal Society, the marvels of witchcraft, sympathetic powders, and other relics of mediaeval superstition disappeared like a mist before the sun, whilst accurate observations and demon strations of a host of new wonders accumulated, amongst which were numerous contributions to the anatomy of animals, and none perhaps more noteworthy than the observations, made by the aid of microscopes constructed by himself, of Leeuwenhoek, the Dutch naturalist (1683), some of whose instruments were presented by him to the society. Results of It was not until the 19th century that the microscope, ascot the thus early applied by Leeuwenhoek, Malpighi, Hook, and Swammerdam to the study of animal structure, was per fected as an instrument, and accomplished for zoology its final and most important service. The earlier half of the 19th century is remarkable for the rise, growth, and full development of a new current of thought in relation to living things, expressed in the various doctrines of develop ment which were promulgated, whether in relation to the origin of individual animals and plants or in relation to their origin from predecessors in past ages. The perfecting of the microscope led to a full comprehension of the great doctrine of cell-structure and the establishment of the facts (1) that all organisms are either single corpuscles (so-called cells) of living material (microscopic animalcules, &c.) or are built up of an immense number of such units; (2) that all organisms begin their individual existence as a single unit or corpuscle of living substance, which multi plies by binary fission, the products growing in size and multiplying similarly by binary fission; and (3) that the life of a multicellular organism is the sum of the activities of the corpuscular units of which it consists, and that the processes of life must be studied in and their explanation obtained from an understanding of the chemical and physical changes which go on in each individual corpuscle or unit of living material or protoplasm (cell-theory of Schwann). Ideas of On the other hand, the astronomical theories of develop- mcnt f the s l ar system from a gaseous condition to its present form, put forward by Kant and by Laplace, had impressed men s minds with the conception of a general movement of spontaneous progress or development in all nature; and, though such ideas were not new but are to be found in some of the ancient Greek philosophers, yet now for the first time they could be considered with a sufficient knowledge and certainty as to the facts, due to the careful observation of the two preceding centuries. The science of geology came into existence, and the whole panorama of successive stages of the earth s history, each with its dis- nient. tinct population of strange animals and plants, unlike those of the present day and simpler in proportion as they recede into the past, was revealed by Cuvier, Agassiz, and others. The history of the crust of the earth was explained by Lyell as due to a process of slow development, in order to effect which he called in no cataclysmic agencies, no mysterious forces differing from those operating at the present day. Thus he carried on the narrative of orderly development from the point at which it was left by Kant and Laplace, explaining by reference to the ascertained laws of physics and chemistry the configuration of the earth, its mountains and seas, its igneous and its stratified rocks, just as the astronomers had explained by those same laAvs the evolution of the sun and planets from diffused gaseous matter of high temperature. The suggestion that living things must also be included The in this great development was obvious. They had been so Natur- included by poet-philosophers in past ages; they were so! included by many a simple-minded student of nature who, * watching the growth of the tree from the seed, formed a true but unverified inference in favour of a general process of growth and development of all things from simpler beginnings. The delay in the establishment of the doctrine of organic evolution was due, not to the ignorant and un observant, but to the leaders of zoological and botanical science. Knowing as they did the almost endless com plexity of organic structures, realizing as they did that man himself with all the mystery of his life and conscious ness must be included in any explanation of the origin of living things, they preferred to regard living things as something apart from the rest of nature, specially cared for, specially created by a Divine Being, rather than to indulge in hypotheses which seemed to be beyond all pos sibility of proof, and were rather of the nature of poets dreams than in accordance with the principles of that new philosophy of rigid adherence to fact and demonstration which had hitherto served as the mainsprings of scientific progress. Thus it was that the so-called &quot; Natur-philoso- phen&quot; of the last decade of the 18th century, and their successors in the first quarter of the 19th, found few adherents among the working zoologists and botanists. Lamarck, Treviranus, Erasmus Darwin, Goethe, and Saint- Hilaire preached to deaf ears, for thejj; advanced the theory that living beings had developed by a slow process of transmutation in successive generations from simpler an cestors, and in the beginning from simplest formless matter, without being able to demonstrate any existing mechanical causes by which such development must necessarily be brought about. They were met in fact by the criticism that possibly such a development had taken place; but, as no one could show as a simple fact of observation that it had taken place, nor as a result of legitimate inference that it must have taken place, rt was quite as likery that the past and present species of animals and plants had been separately created or individually brought into existence by unknown and inscrutable causes, and (it was held) the truly scientific man would refuse to occupy himself with such fancies, whilst ever continuing to concern himself with the observation and record of indisputable facts. The critics did well; for the &quot; Xatur-philosophen,&quot; though right in their main conception, were premature. It was reserved for Charles Darwin, in the year 1859, Darwin s to place the whole theory of organic evolution on a new doctrine footing, and by his discovery of a mechanical cause actu- &quot;. ally existing and demonstrable by which organic evolution must be brought about to entirely change the attitude in regard to it of even the most rigid exponents of the scien tific method. Since its first publication in 1859 the history of Darwin s theory has been one of continuous and decisive conquest, so that at the present day it is universally ac- XXIV. 10 1