be said to regard the deductions of embryology amongst the chief supports of their hypothesis. Hence, as the subject is not merely important in itself, but also somewhat technical in details, it has been judged advisable to discuss the problems of development at some length. In chapter ninth, the earlier stages in the development of animals at large form the chief topics treated. In the tenth section, two special groups-the Echinoderms or star-fishes, &c., and the Crustaceans (or crabs, lobsters, and their allies) are selected for discussion; whilst in the succeeding section attention is directed to the special features observable in the development of the Molluscs, and of higher animals still.

The twelfth chapter, devoted to the "metamorphosis" of insects, is intended specially to show how the development of these animals presents us with a series of highly interesting illustrations of certain modifications affecting the young of animals as well as the adults. The origin of the wings of insects, and other details incidental to the structure and physiology of these animals, are also discussed in this chapter.

The thirteenth chapter revises, somewhat at length, certain problems in the constitution of animals which appear worthy of study; whilst incidentally the nature of the plant-constitution is also treated. Both topics are related to evolution in a broad sense; since the factors which determine the intimate constitution of the animal or plant must also perforce possess a large share of influence in modifying the worlds of life at large.

The fourteenth chapter, dealing with the "fertilisation of flowers," is intended to illustrate certain of the methods whereby, in the physiology and life of plants, the evolution of new races is favoured and assisted. No more typical examples of ways and means adapted to aid and inaugurate the primary conditions on which evolution depends and to ensure variation, could well be cited than this department of botanical science. The deductions from flowerfertilisation tend very powerfully, moreover, to support the doctrine of descent in other phases than those which are connected merely with plant-reproduction at large.

The fifteenth chapter, devoted to the subject of "degeneration," exemplifies the axiom that the ways of evolution include backsliding and retrogression as well as advance. Many animals and plants have developed all their characteristic features through their adoption of, and adaptation to, a lower way of life than that pursued by their ancestors; whilst whole groups of animals present features to the naturalist which could not be accounted for by any ordinary phase of evolution, but which the idea of degeneration, as a factor in working out the ways of life, has fully explained.

The concluding chapter deals with the relations of geological

science to evolution, and sums up certain geological matters and aspects of evolution which have been cursorily alluded to in the preceding sections. The general development of life on the earth, as well as the more special phases with which the geologist has to deal, are shown to support evolution fully and completely. The history of life in the past correlates itself so completely and fully with that of life as it exists to-day, that the geological side of the argument in favour of evolution has come prominently to the front in every system which has had for its aim the exposition of the theory of descent.

It should, lastly, be borne in mind that the evidence for or against the theory of evolution must be judged chiefly by biological standards, and from the biological standpoint, if an accurate estimate of its probabilities, excellencies, and powers to explain satisfactorily the phenomena of life and structure is to be formed. The theory of descent has been frequently criticised, with scant success, however, from other points of view than the biological. But as a theory which, above all else, purports to present us with a rational account of the origin and modifications of living beings, it is evident that its weakness and its strength alike must be sought for within the domain which the naturalist claims as his own. Hence the succeeding pages may be viewed as an attempt to summarise in a popular form the chief details of the evidence, on the fair and rational interpretation of which the evolutionist is well content to rest the claims of his doctrine for intellectual assent and acceptance. In such a study, moreover, may be most readily found the materials for a comprehension of those aspects of the subject which lie somewhat apart from the main pathways of biological study.

The interest of the whole topic need hardly be alluded to in closing these introductory remarks. No subject which can engage the attention of the thinker in these latter days presents so many and varied avenues, leading to allied fields of inquiry, as the doctrine of descent. As applied to man alone, the evolution theory teems with interest, and suggests endless problems for the consideration of the metaphysician, the ethical philosopher, and the sociologist, not to speak of the multifarious features of anatomy, physiology, and geology, which the purely human phase of the theory presents to view. The concluding words of Mr. Darwin in the "Origin of Species" eloquently describe the varied interests which the subject evokes, and also summarise his own conclusions concerning the agencies which have wrought out the existing order of living nature. "It is interesting," says Mr. Darwin, "to contemplate a tangled bank, clothed with many plants of many kinds, with birds singing on the bushes, with various insects flitting about, with worms crawling through the damp earth, and to reflect that these elaborately constructed forms, so different

from each other, and dependent upon each other in so complex a manner, have all been produced by laws acting around us. These laws, taken in the largest sense, being Growth with Reproduction; Inheritance, which is almost implied by reproduction; Variability from the indirect and direct action of the conditions of life, and from use and disuse; a Ratio of Increase so high as to lead to a Struggle for Life, and, as a consequence, to Natural Selection, entailing Divergence of Character, and the Extinction of less improved forms. Thus, from the war of nature, from famine and death, the most exalted object which we are capable of conceiving, namely, the production of the higher animals, directly follows. There is grandeur," concludes Mr. Darwin, "in this view of life, with its several powers having been originally breathed by the Creator into a few forms or into one; and that whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms, most beautiful and most wonderful, have been, and are being evolved."

II.

THE STUDY OF BIOLOGY.

It may reasonably be supposed that every intelligent person is perfectly conversant with the term "Natural History," and with the common meaning usually attached thereto. As employed in ordinary life, or even in scientific circles, where exactness of language is a necessity for the clear expression of thought, the term has come to signify the study of the animal world. Hence, popularly, a "natural historian" is believed to be a person who is much at home in zoological gardens, in aquaria, and in all places where animal life is presented to view, for purposes of study, serious or otherwise. To correct popular and long-standing ideas, is a task for which no sensible person can have any great liking. Albeit that the task is often necessary, and in matters more serious than the nomenclature of science has to be undertaken as a matter of conscience, the work of reforming old-established notions of things is frequently the labour, not of one lifetime, but of many generations. Still, effort is, and must be, cumulative in its effects; and if in the present instance I can succeed in showing the rational use of the name Natural History," I may perchance not merely preface this chapter by a necessary and appropriate explanation, but likewise aid in diffusing better, because truer, ideas of the aim and scope of natural science.

The term "Natural History" finds different meanings according to the latitude in which it is used, and according to the prevailing ideas which the name has been accustomed to convey to the minds of those using the name. In the north, for instance, in academic circles, the name is used to signify "zoology," or the study of animals alone. A student who, in a northern university, attends a class of "Natural History," is understood to concern himself solely with the animal population of the globe. Elsewhere the name has been used to indicate the study of plants and animals together; the student of "Natural History" in this latter sense, extending his researches into the field of "Botany," in addition to that of "Zoology." But a third meaning of the name comes to hand in which it is used, in strict accordance with its etymological significance, to signify, not the study of any one or two departments of nature, but to denote the whole range of natural science studies. Employed in this latter sense, the name "Natural History" is found to include not merely the knowledge of animals and plants, but the

study of minerals and of the inorganic or non-living world at large; whilst it may also be shown to include the study of the planets, because, as a history of nature, it is bound to take account of everything whereof nature consists. To be a "Natural Historian" in this latter sense would imply a man's knowledge of the whole universe. But as human life, in one view at least, is conveniently short, and as wisdom and knowledge are apt to linger long, the most ardent devotees of science may reasonably shrink from laying claim to a full or even moderate knowledge of "Natural History" as thus defined. The "Admirable Crichton" in these days is an unknown creature; and although now and then a master-mind sweeps across the horizon of knowledge-although an occasional century may see a Darwin or a Helmholtz with a profound knowledge of naturescience in well-nigh all its branches-still, the bounds of this wide science of "Natural History," as we have defined it, threaten to prove beyond the powers and grasp of any one mind amongst us.

It will thus be seen that the correct use of the name "Natural History" is that in which it is employed to mean a knowledge of universal nature. This being so, what are the branches which this great science may be said to include? I have already indicated that geology and mineralogy, in addition to astronomy and natural philosophy (or physics), find a natural place within its limits. Chemistry is as truly a branch of natural history as geology, and when we have placed these sciences in the category of the "Natural Historian," there yet remains an important branch which in one sense may be said to unite the others, and which concerns itself with the living things of this world.

The child in his elementary lessons is accustomed to speak of the three kingdoms of nature. This division into animals, plants, and minerals is a perfectly correct method of parcelling out nature's belongings. Although possessing obvious relations with the animals and plants, the sciences of chemistry, geology, and mineralogy deal chiefly with the mineral, or lifeless, section of nature, as does natural philosophy, and its offspring astronomy. It becomes clear, then, that the interests of living things require to be considered under a special department of natural science. In former days, as we have seen, the "Natural Historian" was the scientific guardian of the animal and plant interests. Abolishing this phrase, what term, it may be inquired, do we now employ to indicate the study of living beings? The answer to this question may fitly conclude these introductory remarks. As Huxley has shown in his lecture "On the Study of Biology," whilst the name "Natural History" was used in the broad sense to include all departments of natural knowledge up to the middle of the seventeenth century, the growing specialisation of scientific studies.