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hypothesis in question can suffer from arguments familiar in days when natural theology was strained and wrested to its destruction. A truer and a higher use for the beauty of plants and of animals as well is found in the special advantages which such beauty confers upon the race. In the animal, beauty appears as an aid to the propagation of the species, as it is in the plant; and it is by the action of insects that the beauty of flowers has been extended and developed. The beauty of the blossom is in truth due to the visitations of the insect races which in the past have selected its petals as a feeding-ground, and which have strengthened and increased the flower race, thus favoured by a true "natural selection," in the universal struggle for existence. The higher ideas of nature thus implanted, form no mean fruits of a study of the polity of primroses and other common flowers. Such studies correct the idea that this world is simply a huge workshop, filled with specially contrived mechanical appliances for man's use and benefit, or a gaudy saloon decked out with beauty for the indulgence of his senses. Those who hold such views may not complain if their belief be logically extended to include the theory that fur-seals were specially created to afford us seal-skin jackets, and humming-birds designed to trim the hats of fair wearers in the fleeting fashion of the hour. So that, if no greater excellence be traceable in the theory of evolution than is involved in the correction of false notions of the aims and ends of nature, those who pursue science-studies even to this extent will reap a rich harvest of rational ideas concerning the true ordering of this universe, especially within the domain of life itself.

XV.

THE EVIDENCE FROM DEGENERATION.

IT cannot be gainsaid that a survey of the fields of life around us impresses one with the idea that the general tendencies of living nature gravitate towards progression and improvement, and are modelled on lines which, as Von Baer long ago remarked, lead from the general or simple towards the definite, special and complex. This much is admitted on all hands, and the ordinary courses of life substantiate the aphorism that progress from low grades and humble ways is the law of the organic universe that hems us in on every side, and of which, indeed, we ourselves form part. The growth of plantlife, which runs concurrently with the changing seasons of the year, impresses this fact upon us, and the history of animal development but repeats the tale. In the passage from seed to seed-leaf, from seed-leaf to stem and leaves, from simple leaves to flower, and from flower to fruit, there is exhibited a natural progress in plant existence, which testifies eloquently enough, by analogy at least, to the existence of like tendencies in all other forms of life. Similarly, in the animal hosts, progressive change is seen to convert that which is literally at first" without form and void" into the definite structure of the organism. A minute speck of protoplasm on the surface of the egg -a speck that is indistinguishable, in so far as its matter is concerned, from the materies of the animalcule of the pool—is the germ of the bird of the future. Day by day the forces and powers of development weave the protoplasm into cells, and the cells, in turn, into bone and muscle, sinew and nerve, heart and brain. In due season the form of the higher vertebrate is evolved, and progressive change is once more illustrated before the waiting eyes of life-science. But the full meaning of most of the problems which life-science presents to view is hardly gained by a merely cursory inspection of what may be called the normal side of things. The by-paths of developmentmore frequently, perhaps, than its beaten tracks-reveal guiding clues and traces of the manner in which the progress in question has come to pass. So, also, the side avenues of biology open up new phases of, it may be, the main question at issue, and may reveal, as in the present instance, an interesting reverse to the aspects we at first deem of sole and paramount importance. For example, a casual study of the facts of animal development is well calculated to show that life is not all progress, and that it includes retrogression as well

as advance. Physiological history can readily be proved to tend in many cases towards backsliding, instead of reaching forwards and upwards to higher levels. This latter tendency, beginning now to be better recognised in biology than of late years, can readily be shown to exercise no unimportant influence on the fortunes of animals and plants. In truth, life at large must now be regarded as existing between two great tendencies-the one progressive and advancing, the other retrogressive and degenerating. Such a view of matters may serve to explain many things in living histories which have hitherto been regarded as somewhat occult and difficult of solution; whilst we may likewise discover that the coexistence of progress and retrogression is a fact perfectly compatible with the lucid opinions and teachings concerning the origin of living things which we owe to the genius of Darwin and his disciples.

A fundamental axiom of modern biology declares that in the development of a

living being we may discern a panoramic unfolding, more or less complete, of its descent. "Development repeats descent" is an aphorism which, as we have seen, cultured biology has everywhere writ large over its portals. Rejecting this view of development and its teachings, the phases! through which animals and plants pass in the course of their progress from the germ to the adult stage present themselves to view as simply meaningless facts and useless freaks and vagaries of nature. Accepting the ideafavoured, one may add, by every circumstance of life-science-much that was before wholly inexplicable becomes plain and readily understood. And the view that a living being's development is really a quick and often abbreviated summary of its evolution and descent, both receives support from and gives countenance to the general conclusion

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FIG. 241.-DEVELOPMENT OF FROG.

that life's forces tend as a rule towards progress, but likewise exhibit retrogression and degeneration. If a living being is found to begin its history, as all animals and plants commence their existence, as a speck of living jelly, comparable to the adult animalcule of the pool, it is a fair and logical inference that the organisms in question have descended from lowly beings, whose simplicity of structure is repeated in the primitive nature of the germ. If, to quote another illustration, the placid frog of to-day, after passing through its merely protoplasmic stage, appears before us in the likeness of a gill-breathing fish (Fig. 241), the assumption is plain and warrantable that the frog race has descended from some primitive fish stock, whose likeness is reproduced with greater or less exactness in the tadpoles of the ditches. Or if, to cite yet another example, man and his neighbour quadrupeds (Fig. 242), birds, and reptiles, which never breathe by gills at any period of their

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existence, are found in an early stage of development to possess "gillarches" (g), such as we naturally expect to see, and such as we find in the fishes themselves, the deduction that these higher animals are descended from gill-bearing or aquatic ancestors seems to admit of no reasonable denial. On any other theory, the existence of gill-arches in the young of an animal which never possesses gills is to be viewed as an inexplicable freak of nature-a dictum which, it is needless to remark, belongs to an era one might well term prescientific, in comparison with the "sweetness and light" of these latter days.

Hanging very closely on the aphorism respecting development and its meaning, is another biological axiom, well-nigh as important as the former. If development teaches that life has been and still is progressive in its ways, and that the simpler stages in an animal's history represent the conditions of its earliest ancestors, it is a no less stable proposition that at all stages of their growth living beings are subject to the action of outward and inward forces. Every living organism lives under the sway and dominance of forces acting upon it from without, and which it is enabled to modify and to utilise by its own inherent capabilities of action. It is, in fact, the old problem

of the living being and its surroundings applied to the newer conceptions of life and nature which modern biology has revealed. The living thing is not a stable unit in its universe, however wide or narrow that sphere may be. On the contrary, it exists in a condition of continual war, if one may so put it, between its own innate powers of life and action, of living and being, and the physical powers and conditions outside. This much is now accepted by all scientists. Differences of opinion certainly exist as to the share which the internal constitution of the living being plays in the drama of life and progress. It seems, however, most reasonable to conclude that two parties exist to this, as to every other bargain; and regarding the

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animal or plant as plastic in its nature, we may assume such plasticity to be modified on the one hand by outside forces, and on the other by internal actions proper to the organism as a living thing. Examples of such tendencies of life are freely scattered everywhere in nature's domain. For instance, we know of many organisms which have continued from the remotest ages to the present time, without manifest change of form or life, and which appear before us to-day, the living counterparts of their fossilised representatives of the Chalk or it may be of Silurian or Cambrian times. The lampshells (Terebratula) of the Chalk exist in our own seas with well-nigh inappreciable differences. The Lingula or Lingulella (Fig. 243, a), another genus of these animals, has persisted from the Cambrian age

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