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and the Snow-flake is equally local. Gagea lutea is a rare plant of the Oxfordshire hills, yet it reappears in the Himalaya ; Gentiana lutea is found on the high slopes of the Puy de Dôme, but it is deficient over the greater part of central France, and is rare even in the direction of the Alps till we reach the mountains where it occurs more frequently. Instances like these which have been now enumerated, seem to be satisfactory in proof that the actual distribution of any given species is the final result of many long periods of general effort to extend, and of some particular influences to restrain, its diffusion.
Remarkable examples are recorded by botanists of plants having sprung up unexpectedly in the course of cultivation, in spots where such had not been growing for very long periods. Perhaps the well-known case of the upspringing of white clover on the burnt surface of the heaths of Yorkshire, when lime has been added, is one of the most striking. The heath thus displaced has been growing there for many centuries ; the little clover is rarely seen in the district; yet no sooner is the heath expelled and the calcareous element added, than it grows and covers the surface.
The distribution of particular groups of animals is quite as limited as that of plants, and this is true not only for land-animals but for the inhabitants of
the sea and the free wanderers of the air. While some genera are of very wide occurrence in the sea, as the little Spirula, and the huge Physeter; while some birds pass from arctic to temperate, and from temperate to torrid zones, and some quadrupeds annually migrate over large breadths of land in quest of food, the far greater number appear to be restrained by necessity or limited by choice to narrow tracts and definite associations of life.
It is not by conformity of climate or physical conditions, or oceanic currents, that the few existing genera of Brachiopoda are now allowed representatives in almost all seas, for each particular species of these genera is usually limited to one small area, or zone of ocean. Rhynchonella psittacea to the circumpolar seas ; Terebratula vitrea to the Mediterranean; and Waldheimia australis to the shore of New Holland
Reptilia in a general sense depend for their distribution on favourable climate; but when we examine any certain group, as the Crocodilidæ, one species is found to belong to the Nile, another to the Ganges, a third to the North American rivers. Struthious birds wander over the dry lands of several
See on questions of Distribution of Mollusca, Woodward's Rudimentary Treatise on Recent and Fossil Shells,--an excellent work.
parts of the world, but the Rhea is found in South America, the Ostrich in Africa and Arabia, the Cassowary in the Indian Islands, and the Emeu in Australia.
The Condor clings to the summits of the Cordillera, the Lammergeyer haunts the Alps—the Stork knoweth her abiding place. In a word, every living race of plants and animals exists in a province of space; over which by natural conditions it has been diffused, within which by natural conditions it has been restrained, and beyond which it only passes by a change of these conditions. Thus one place of origin is indicated for each species of plant and animal—one locality where it first appeared, whether it still remain there confined to a limited region, or have wandered far away, without losing its prominent characters, through length of time, change of conditions, mixture with other races, or any of the innumerable incidents of the struggle for existence.'
I have thus, Mr Vice-Chancellor, recapitulated some of the laws regarding the Conditions and Limitations of Life, which are commonly accepted among naturalists, and must be observed by geologists who desire to work out the problem of the succession of ancient created being. I propose them as the very reverse of novelties, and regard them
as truths generally admitted. Here in Cambridge, I know that these and other great results of the contemplation of nature are well comprehended, since you have all long had the advantage of hearing them from the eloquent lips of the noblest of English Geologists, your pride and my pride—Professor Sedgwick. Assuming, then, definite limits and conditions for every living form; a definite local origin, and a longc-ontinued permanence of structure and habits for each species of plant and animal, I may now turn to the appointed purpose of this lecture, and trace the history of the changes of life in the ancient lands and seas.
TYPES OF LIFE STRUCTURE.
One of the most arduous of all the enterprises of science is the attempt to classify the variously allied objects of organic and inorganic nature, according to their prevalent structures and qualities—to place them in such relations to each other as they really have to represent, in short, the plan of these parts of creation-according to the leading ideas of which it is, or seems to us to be, the expression. Not that so great a purpose was at first conceived by Aristotle and his followers, or even by Linnæus, or Cuvier; it was at first intended to group together things which resembled each other,-as crystals-herbs—trees ;residents in the water--animals of the land. Pro
ceeding from such analogies to stricter inquiries, other and firmer divisions were founded on the organs of motion, prehension, food, respiration and circulation,—the organs of sense, and the internal arrangements of the nervous system. In the course of these inquiries we have detected, under many disguises, some general rules of structure and function -patterns or types so to speak to each of which a vast number of specific forms can be referred, as if they were so many examples of one general structure, modified in an almost infinite variety of ways to suit appointed habits of life. The general characters of agreement we often call typical, the special characters of difference are often called adaptive—terms which imply the recognition of law and modification, mind and choice-a Creator who works by rule, and who has provided for wonderful diversity in his works and for the persistence through them all of some firm general principles of construction, which can be traced out in their operation by the human mindprocess of observation, comparison, and inference.
When reduced to the smallest number of great primary types, we find Plants to be ranked in two divisions :
Phanerogamous or flowering and seed-bearing, and Cryptogamous or flowerless plants deficient of true seeds.