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and animal in a primitivo stock, which reproduces its like from generation to generation, and so continues the species. Taking the idea of species from this perennial succession of essentially similar individuals, the chain is logically traceable back to a local origin in a single stock, a single pair, or a single individual, from which all the individuals composing the species have proceeded by natural generation. Although the similarity of progeny to parent is fundamental in tho conception of species, yet the likeness is by no means absolute; all species vary more or less, and some vary remarkably-partly from the influence of altered cir cumstances, and partly (and more really) from unknown constitutional causes which altered conditions favor rather than originate. But these variations aro supposed to be mere oscillations from a normal state, and in Nature to be limited if not transitory; so that the primordial differences between species and species at their beginning have not been effaced, nor largely obscured, by blending through variation. Conse quently, whenever two reputed species are found to blend in Nature through a series of intermediate forms, community of origin is inferred, and all the forms, however diverse, are held to belong to one species. Moreover, since bisexuality is the rule in Naturo (which is practically carried out, in the long run, far more generally than has been suspected), and the heritable qualities of two distinct individuals are mingled in the offspring, it is supposed that the general

"Species tot sunt, quot diversas formas ab initio produxit Infini tum Ens; quæ forme, secundum generationis inditas leges, produxeru plures, at sibi semper similes."-Linn. Phil. Bot., 99, 157.

sterility of hybrid progeny interposes an effectual barrier against the blending of the original species by crossing.

From this generally-accepted view the well-known theory of Agassiz and the recent one of Darwin diverge in exactly opposite directions.

That of Agassiz differs fundamentally from the ordinary view only in this, that it discards the idea of a common descent as the real bond of union among the individuals of a species, and also the idea of a local origin-supposing, instead, that each species origi nated simultaneously, generally speaking, over the whole geographical area it now occupies or has occupied, and in perhaps as many individuals as it numbered at any subsequent period.

Mr. Darwin, on the other hand, holds the orthodox view of the descent of all the individuals of a species not only from a local birthplace, but from a single ancestor or pair; and that each species has extended and established itself, through natural agencies, wherever it could; so that the actual geographical distribution of any species is by no means a primordial arrangement, but a natural result. He goes farther, and this volume is a protracted argument intended to prove that the species we recognize have not been independently created, as such, but have descended, liko varieties, from other species. Varieties, on this view, are incipient or possible species: species are varieties of a larger growth and a wider and earlier divergence from the parent stock; the difference is one of degree, not of kind.

The ordinary view-rendering unto Cæsar the

things that are Cresar's-looks to natural agencies for the actual distribution and perpetuation of species, to a supernatural for their origin.

The theory of Agassiz regards the origin of species and their present general distribution over the world as equally primordial, equally supernatural; that of Darwin, as equally derivative, equally natural.

The theory of Agassiz, referring as it does tho phenomena both of origin and distribution directly to the Divine will-thus removing the latter with the former out of the domain of inductive scienco (in which eflicient cause is not the first, but the last word) -may be said to be theistic to excess. The contrasted theory is not open to this objection. Studying the facts and phenomena in reference to proximate causes, and endeavoring to trace back the series of cause and effect as far as possible, Darwin's aim and processes are strictly scientific, and his endeavor, whether successful or futile, must be regarded as a legitimate attempt to extend the domain of natural or physical science. For, though it well may be that "organic forms have no physical or secondary cause," yet this can be proved only indirectly, by the failure of every attempt to refer the phenomena in question to causal laws. But, however originated, and whatever bo thought of Mr. Darwin's arduous undertaking in this respect, it is certain that plants and animals are subject from their birth to physical influences, to which they have to accommodate themselves as they can. How literally they are "born to trouble," and how incessant and severe the struggle for life generally is, the present volume graphically describes. Few will

deny that such influences must have gravely affected
the rango and the association of individuals and species
on the earth's surface. Mr. Darwin thinks that, acting
upon an inherent predisposition to vary, they have suf-
ficed even to modify the species themselves and pro-
duce the present diversity. Mr. Agassiz believes that
they have not even affected the geographical range
and the actual association of species, still less their
forms;
but that every adaptation of species to climate,
and of species to species, is as aboriginal, and therefore
as inexplicable, as are the organic forms themselves.

Who shall decide between such extreme views so ably maintained on either hand, and say how much of truth there may be in each? The present reviewer has not the presumption to undertake such a task. Having no prepossession in favor of naturalistic theo ries, but struck with the eminent ability of Mr. Darwin's work, and charmed with its fairness, our humbler duty will be performed if, laying aside prejudico as much as we can, wo shall succeed in giving a fair account of its method and argument, offering by the way a few suggestions, such as might occur to any naturalist of an inquiring mind. An editorial charac ter for this article must in justice be disclaimed. Tho plural pronoun is employed not to give editorial weight, but to avoid even the appearance of egotism, and also the circumlocution which attends a rigorous adherence to the impersonal style.

We have contrasted these two extremely divergent theories, in their broad statements. It must not be inferred that they have no points nor ultimate results in cominon.

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In the first place, they practically agree in upset ting, each in its own way, the generally-received dofinition of species, and in sweeping away the ground of their objective existenco in Nature. Tho orthodox conception of species is that of lineal descent: all tho descendants of a common parent, and no other, constitute a species; they have a certain identity becauso of their descent, by which they are supposed to bo recognizable. So naturalists had a distinct idea of what they meant by the term species, and a practical rule, which was hardly the less useful because diflicult to apply in many cases, and because its application was indirect: that is, the community of origin had to be inferred from the likeness; such degree of similarity, and such only, being held to be conspecific as could be shown or reasonably inferred to be compatible with a common origin. And the usual concurrence of the whole body of naturalists (having the samo data be fore them) as to what forms are species attests the value of the rule, and also indicates some real foundation for it in Nature. But if species were created in numberless individuals over broad spaces of territory, these individuals are connected only in idea, and species differ from varieties on the one hand, and from genera, tribes, etc., on the other, only in degree; and no obvious natural reason remains for fixing upon this or that degree as specific, at least,no natural standard, by which the opinions of different naturalists may bo correlated. Species upon this view are enduring, but subjective and ideal. Any three or more of the hu man races, for example, are species or not species, according to the bent of the naturalist's mind. Darwin's

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