every element-earth, air, and ocean-and even finding their abodes as parasites on other animals, the articulata have a function as diversified as their organisation. They

are vegetable as well as animal feeders, and occur in every region, though culminating in numbers, size, and specific variety under the genial influences of equatorial and tropical latitudes. Their world-office is mainly biological; and while preying alike on plants and animals, they become in turn the principal food of other creatures-fishes, birds, reptiles, and mammals. Lastly, and highest and most diver

sified in structure, come the Vertebrata-the fishes, reptiles, birds, and mammals - the inhabitants of every element, and the tenants of every region, though culminating chiefly in numbers and rank within temperate and warm parallels.

In general terms, the ascent in the zoological scale is from the aquatic to the terrestrial, from the cold-blooded waterbreathers to the cold-blooded air-breathers, and from these to the still higher warm-blooded air-breathers. The great majority of invertebrate forms are confined to the waters: a large proportion of the vertebrates are strictly terrestrial, or own an amphibious existence. Between them and the higher forms of terrestrial vegetation, the interdependence is complete; the existence of the higher flora being unintelligible in the absence of a higher fauna. The grasses,

foliage, seeds, fruits, and roots of the one kingdom become the indispensable sustenance of the vegetable-feeders of the other; while the vegetable-feeders in turn become the food of the carnivora. Among the vertebrata the actions and reactions of life are more immediate and apparent, and in them alone are manifested all the higher offices of vitality. Sense, instinct, volition, reason, and moral perception, mark the line of ascent. The vital predominates over the material, and in the culminating order (Bimana) the psychological rise superior to the physiological functions.

Such are the leading divisions of the animal kingdom, which are again divided and subdivided into families, and genera, and species-each minor group presenting a distinct and determinate pattern on the great web of created existence. By a study of these patterns, and a knowledge of their manifold relations, the zoologist is enabled to arrive. at some intelligible idea of the scheme of existing vitality; and so, possessed of similar knowledge, the palæontologist strives to reunite his scattered fragments, and to assign to them their proximate place in the still greater scheme which combines the present with the past, and the forms that have become extinct with those that still flourish around us. In the study of Fossil Zoology, or PalæoZoology, as it is termed, much more satisfactory progress has been made than in the sister department of Fossil Botany, the harder structures of animals (corals, shells, crusts, scales, scutes, teeth, and bones) being better preserved than the softer and more perishable tissues of vegetation. It is true that many of these fragments are widely scattered and sorely mutilated, that marine forms are relatively more abundantly retained than those of terrestrial origin, that only the merest specks of the fossiliferous strata have yet been examined, and that the sea now rolls over strati

fied areas vastly more extended than those that lie patent to geological research. Still, in face of all these obstructions and imperfections, palæontology has wonderfully enlarged our conceptions of vitality, has opened up to the present age a theme altogether unknown to our ancestors, and, guided by a true knowledge of the present, is destined yet to unfold a fuller and fairer vision of the life that has gone before us. As the zoologist pushes his discoveries into space, so the paleontologist pushes his discoveries into time. As the former turns to unexplored regions in the hope of finding new forms, so the latter turns to unexplored formations-formations whose areas are as varied as their dates, and whose strata give promise of other and other life-revelations for centuries yet to come.

3.-CO-ADAPTATIONS OF FLORA AND FAUNA.

Perfect as the existing flora and fauna may appear, each in its own proper line, they are only constituent portions of a greater life-system, bound together by numerous coadaptations and adjustments. As each is adapted to, as well as dependent on, external conditions, so both are dependent on one another, and, as presently constituted, neither could possibly enjoy a separate existence. Both, for example, are incessantly dependent on the atmosphere, yet the oxygen which the plant exhales is inhaled by the animal, and the carbonic acid expired by the animal is absorbed and assimilated by the plant. The plant rooted in the soil and casting abroad its leaves and branches in the atmosphere, though seemingly deriving the main elements. of its growth from inorganic sources, is nevertheless stimulated into life and exuberance by the presence of organic decay; while the animal, being herbivorous, subsists im

mediately upon plants, or, if carnivorous, preys upon the plant-feeders, and is thus also ultimately dependent on the vegetable world for its subsistence. The law of circulation and interdependence is complete; and no portion of the circle could be removed without a corresponding change in the characters of the vegetable and animal kingdoms. Again, many plants are dependent on the locomotive powers of animals for their wider dispersion and increase; while other animals acquire a wider range through this new and increased source of subsistence. Further, as many animals, in their habits and organisation, are altogether fitted for an arboreal existence, the destruction of the tree would involve the destruction or non-existence of this peculiar organisation; and as other creatures are specially fitted to live on certain fruits, leaves, and roots, the disappearance of these specific supplies would necessarily involve the annihilation of the consumers. As in existing nature these and many other similar adaptations are fixed and certain, and we may safely reason from cause to effect and from effect to causation, so, in the ancient world, we may rely on similar adjustments-reasoning from certain phases of plant and animal life to the conditions under which they must have existed, and from the presence of certain races of plants and animals to the existence of other plants and animals to which they were necessarily co-adapted. It is thus that the study of the Past becomes hopeful, and Palæontology assumes the character of an inductive and reliable science. The Present is ever the safest guide to the Past; the Extinct is ever most clearly illuminated by the light reflected from the Existing.

E