There are differences, also, in the periods of the acquirement of the perfect plumage, the size and shape of the eggs, the nature of flight, and the powers of flight, so-called ' homing' birds having enormous flying powers; while on the other hand, the little tumbler is so called because of its extraordinary faculty of turning head-over-heels in the air, instead of pursuing a distinct course. And lastly, the dispositions and voices of the birds may vary. Thus the case of the pigeons shows you that there is hardly a single particular, whether of instinct or habit, or bony structure, or of plumage, of either the internal economy or the external shape, in which some variation or change may not take place, which by selective breeding may become perpetuated and form the foundation of and give rise to a new race." Nor is this variation confined to domestic animals. Wild species both of plants and animals vary, become diversified, and give rise to new varieties. As many as 28 varieties of oak have been made out within the limits of a single species. The wolf species exhibits some 15 varieties, and lions, tigers, bears, hyenas, foxes, birds, reptiles, and fishes all exhibit marked varieties, which show that wild species undergo modification in a state of nature.

What was needed to make out the analogy of variation between wild and domesticated animals was to discover some process in nature which is the equivalent of human agency in breeding. Mr. Darwin believes that he has discovered this process, and calls it the princi-ple of "natural selection." He says that living beings in a state of nature are subject to certain external conditions, such as climate, situa-tion, character of soil, and exposure to enemies, by which they are surrounded and limited. They are endowed with enormous powers of increase, so that any one of the hundreds of thousands of species of plants or animals, if all its progeny were preserved, would go on multiplying until it covered the earth or filled the sea. Space is fixed and food limited, and the consequence is a universal conflict, the war of races; and in the struggle for existence multitudes perish and comparatively few survive. This survival is not a matter of chance. Mr. Darwin maintains that it is regulated by law, and that those only survive which are in some way best adapted to the conditions of life. The strongest, the fleetest, the most cunning, and the best adapted to the conditions will live and multiply, while the less fit will disappear.

The introduction of European plants and animals into New Zealand affords an instructive example of how races encroach on each other's areas, the weaker being extirpated by the stronger in the competition for existence. Dr. Hooker says: The cow grass has taken possession of the roadsides; dock and water cress choke the rivers; the sow thistle is spread over all the country, growing luxuriantly up to 6,000 feet?; white clover in the mountain districts displaces the native grasses; and the native (Maori) saying is: 'As the white man's rat has driven away the native rat, as the European fly drives away our own, and the clover kills our fern, so will the Maoris disappear. before the white man himself.' Mr. Darwin in his works gives a great number of facts showing how apparently trifling variations give advantages to their possessors, which determine their survival and become perpetuated in the race. The principle of natural selection, or, as it is termed by Herbert Spencer, the survival of the fittest," is now generally recognized as a genuine agency or vera causa, and the opponents of development admit that it may give rise to varieties, although they deny that it is competent to produce the deeper diversities of species.

The extent of its operation remains yet to be determined, but many naturalists agree with Prof. Helmholtz that Mr. Darwin has contributed to science an essentially new creative idea." Mr. Darwin, however, does not assume to be the discoverer of the principle of natural selection, and he points out that others before him have recognized the action of the process, though without seeing its full significance. What he claims is to have first shown the efficacy of the principle in producing divergency of types under the laws of variation and heredity. But having discovered a new factor in organic development, and published his work on the Origin of Species" at the fortunate moment when naturalists had become widely dissatisfied with the old views, he became prominently identified with the development doctrine, and this has led many into the error of regarding Darwinism as the equivalent of evolution, of which, as we are now to see, it is but a minor part.-The advance of civilization in the historical period gave rise to the modern idea of progress, which was strengthened by the discoveries made early in the present century concerning the past course of terrestrial life.

The process was crudely conceived, in the one case as the successive development of all living creatures in a graded and linear series, and in the other case as the continuous movement of humanity toward a state of final perfection. About the year 1850 Mr. Herbert Spencer entered upon the systematic study of the subject. The problem was strictly a scientific one, and he had a wide and accurate preparation for it by a mastery of scientific knowledge which Mr. Mill has pronounced encyclopaedic." Mr. Spencer was also remarkable for his power of analysis, his grasp of wide-reaching principles, and his independence of opinion. The essence of progress is change. Mr. Spencer asked what, then, are the laws of change by which it is effected? Complying with the Newtonian canon that the fewest causes possible are to be assumed in the explanation of phenomena, he took up the question as resolvable in terms of matter, motion, and force. Progress being a theory of the successive changes by which things are produced, his task was to ascertain the dynamical conditions or laws under which the forms of nature rise, continue, and disappear. The objects of nature coexist and are maintained in a certain order in space. Newton discovered that this is effected by the operation of a simple and universal law.