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Show CHAP. XII. PHICAL DISTIUBUTION. 410 GEOGRA . 'b t d to our no t hca: ving as yet discohv ere.d fairly be attn u e . th -"orms which are t ermn d. t deposit e 1 ' · in an interme Ia e b d below : so In space, h. h cur a ove an . h absent, but w IC oc 1 rule that the area In a- it certa1. nl y I·S the gen. era by a group of speCi·e s, I·S · 1 pecies or bited by a sing e s ' t' s which are not rare, d the excep lOll ' b continuous; an ted to show, be accounted for Y may as I have attemp · d under different con- ' me former perio migration at so . 1 eans of transport, and by the d1.t.w ns or by occas1ona mt' t ·n the intermed 1' at e t rae t s. . h . become ex Inc 1 . species aving ies and groups of speCies Both in time and space.' spec development. Groups of - · ' t of maXImUm . have thmr pm~ s . h t a certain period of time, or species, b~longing eit ~~e: characterised by trifling chato a cer~ain area, are o f scul ture or colour. In lookracters In common, as ~ p es as in now looking to ing to the long' successionh oft atgh 'world we find that · throug ou e ' distant pro~Ince~.f£ r little whilst others belonging to a some organisms I e diffe;ent order, or even only to a different class, or to a d ell' .cl'er greatly. In 'l f' the same or er, w differen. t famid y o e the 1o wer m embers of each class both time an ~pac han the higher ; but there are generally change less t ions to the rule. On my in both cases marked ex?ept hrou ·hout time and space theory these several relations t 1 g1 t the forms of life are 1· ntel1i'g 1'b l e'. £o r whether we oo r· e0 ages w1. th1. n t he d d · success1v which have change uringd t those which have f the worl or 0 · same quarter o . ' d . t di'stant quarters, m f h · migrate 111 o changed a ter aving . . h class have been con-both cases the forms within eac . eneration ; and nected by the same bond of ord~nareyla~ecl in blood, the the more near1 y any two forms are r h other I.n tu· ne nearer they will generally stand tof eac iation have been and space; in both c.ases ~he l~ws obe:~ accumulated by the same, and modifications a~e the same power of natural selection. CHAP. XIII. CLASSIFICATION. 411 CHAPTER XIII. MuTUAL AFFINI'l'IES oF OnGANic BEINGS: MoRPHOLOGY: EMBRYOLOGY : RUDIMENTARY ORGANS. CLASSIFICATION, groups subordinate to groups- Natural systemRules and difficulties in classification, explained on the theory of descent with modification- Classification of varieties- Descent always used in classification- Analogical or adaptive characters - Affinities, general, complex and radiating - Extinction separates and defines groups- MoRPHOLOGY, between members of the same class, between parts of the same individualEMBH. YOLOGY, laws of, explained by variations not supervening at an early age, and being inherited at a corresponding age~ Hum~mNTARY ORGANS; their origin explained- Summary. FROM the first dawn of life, all organic beings are found to resemble each other in descending degrees, so that they can be classed in groups under groups. This classification is evidently not arbitrary like the grouping of the stars in constellations. The existence of groups would have been of simple signification, if one group had been exclusively :fitted to inhabit the land, and another the water ; one to feed on flesh, another on vegetable matter, and so on ; but the case is widely different in nature ; for it is notorious how commonly members of even the same sub-group have different habits. In our second and fourth chapters, on Variation and on Natural Selection, I have attempted to show that it is the widely ranging, the much diffused and common, that is the dominant species belonging to the larger genera, which vary most. The varieties, or incipient species, thus produced ultimately become converted, as I believe, into new and distinct species ; and these, on the principle of inheritance, tend to produce other new and dominant · T 2 |