ZOOLOGY 817 pervading element of the protoplasm cannot at present be identified with any visibly separable part of the cell-sub stance, which consists of a hyaline denser network of ex cessive tenuity, of a less dense hyaline liquid, and of finest and less fine granules of varying chemical nature. This "critical" substance, sometimes called "true protoplasm," should assuredly be recognized by a distinct name " plasmo- gen," whilst protoplasm retains its structural connotation. la.smo- The study of the process of fertilization and of the gy- significance in that process of the distinct parts of the sperm-cell and egg-cell the separate fibrilke and granules of the nuclei of those cells at the present moment forms one of the engrossing subjects of zoological investigation. 1 Not less important is the descent, as it were, of physiological investigation in relation to every organ into the arena of the cell : digestion, secretion, muscular contraction, nerve action, all are now questions of plasmology, or the study of cell-substance founded by Schwann. 2 GENERAL TENDENCY OF ZOOLOGY SINCE DARWIN. io- The serious and broadly-based study of bionomics Hnics. w hich was introduced by Darwin, and in his hands gave rise to the doctrine of natural selection, by which the hypothesis of the origin of species by gradual transmutation in the natural process of descent from ancestral forms was established as a scientific doctrine, can hardly be said to have had any history. Buffon (1707-1788) alone among the greater writers of the three past centuries emphasized that view of living things which we call "bionomics." Buffon deliberately opposed himself to the mere exposition of the structural resemblances and differences of animals, and, disregarding classification, devoted his treatise on natural history to a consideration of the habits of animals and their adaptations to their surroundings, whilst a special volume was devoted by him to the subject of reproduction. In special memoirs on this or that animal, and in a subor dinate way in systematic works, material is to be found helping to build up a knowledge of bionomics, but Buffon is the only prominent writer who can be accorded historic rank in this study. 3 The special study of man in these relations such as is concerned with the statistics of population must be considered as having contributed very importantly to Darwin s wider study of bionomics in general. The work of Malthus On Population (1798) exercised the most important influence on Darwin s thought, as he himself tells us, and led him to give attention to the facts of animal population, and so to discover the great moving cause of natural selection the struggle for exist ence. Darwin may be said to have founded the science of bionomics, and at the same time to have given new stimulus and new direction to morphography, physiology, and plas mology, by uniting them as contributories to one common biological doctrine the doctrine of organic evolution itself but a part of the wider doctrine of universal evolu tion based on the laws of physics and chemistry. The full influence of Darwin s work upon the progress and direction of zoological study has not yet been seen. The immediate result has been, as pointed out above, a reconstruction of the classification of animals upon a genealogical basis, and an investigation of the individual development of animals in relation to the steps of their gradual building up by cell-division, with a view to obtain- eleo- ing evidence of their genetic relationships. On the other gy- hand, the studies which occupied Darwin himself so largely subsequently to the publication of the Origin of Species, 1 See the memoirs of Weismaim oil Heredity and F. M. Balfour s Embryology. - For a fuller and general history of PHYSIOLOGY, see that article. 3 The main literary sources made use of by Darwin are the magazines and treatises of horticulturists, farmers, pigeon-fanciers, and the like, in fact what is comprised in the Field newspaper. viz., the explanation of animal (and vegetable) mechanism, colouring, habits, &c., as advantageous to the species or to its ancestors in fact, the new teleology, has not yet been so vigorously pursued as it must be hereafter. The most important work in this direction has been done by Fritz Miiller (Filr Darwin), by Herman Miiller (Fertilization of Plants by Insects), and by August Weismann (memoirs trans lated by Meldola). Here and there observations are from time to time published, but no large progress has yet been made, probably on account of the fact that animals are exceedingly difficult to keep under observation, and that there is no provision in universities and like institutions for the pursuit of these inquiries or even for their academic representation. More has been done with plants than with animals in this way since Darwin, probably owing to the same cause which has, ever since the revival of learning, given botany a real advantage over zoology, namely, the existence of " physick " gardens, now become " botanical " gardens, and the greater ease of management, experiment, and observation in the case of plants than in that of ani mals. It is true that zoological gardens have existed for the last fifty years in all large European cities, but these have always been conducted with a view to popular exhibition; and, even where scientific influences have been brought to bear on their management, they have been those of the morphographer and systematist rather than of the bionomist. Moreover, zoological gardens have never been part of the equipment of the university professor of zoology, as it may be hoped in future will be the case. The foundation of marine biological laboratories under the control of scientific zoologists offers a prospect of true bionomic observation and experiment on an increased scale in the near future, and, were such laboratories founded in our universities and provided with the necessary appliances for keeping terrestrial and freshwater animals, as well as marine forms, alive and under observation in conditions resembling as nearly as possible those of nature, a_ step would have been taken towards carrying on the study of bionomics which cannot long be delayed. It seems to be even more important that the academic curriculum of zoology should not, by mere mechanical adhesion to the old lines of morphography, and experimental research on the chemical and physical properties of tissues and organs, confine the attention and training of young students to what are now, comparatively speaking, the less productive lines of research. If we turn to the other branch of bionomics, that con Threm- cerned with the laws of variation and heredity (thremma- mat - tology), we find that since Darwin, and independently of his own work, there has been a more obvious progress than in teleology. In the first place, the continued study of human population has thrown additional light on some of the questions involved, whilst the progress of microscopical research in the hands of Biitschli, Hertwig, Balfour, and August Weismann promises to give us a clear foundation as to the structural facts connected with the origin of the egg-cell and sperm-cell and the process of fertilization. This is not the fitting place in which to give a sketch of the doctrines and hypotheses of thremmatology. They maybe gathered from Darwin s writings,, more especially the Origin of Species and Animals and Plants under Domes - tication.^ They relate to the causes of variation in animals and plants, the laws of the transmission of parental char acters, the share of each parent in the production of the char acters of the offspring, atavism, and the relations of young to parents as to number, sex, nourishment, and protection. An important development of Darwin s conclusions is actually in progress and deserves special notice here, as it 4 The reader is also referred to Ribot s L lleredite, and the writings of Charles Darwin s cousin, Francis Galton.
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