ch. iv.] THE LAW OF EVOLUTION. 355 



of equal size, and that their segregation results from their 

 like relations to the incident force. The integration of several 

 spinal vertebrae into a sacrum, as the result of exposure to a 

 continuous strain in the same direction, is a still better 

 example ; and from the phenomena of morphological develop- 

 ment many parallel cases might be cited. Wherever dif- 

 ferent (jarts of any group of units stand in different relations 

 to an Incident force, differentiation must result ; and wher- 

 ever any sub-group of these units, after becoming unlike the 

 rest, is acted on by a common force, the result must be 

 the integration of the sub-group. But manifestly the pri- 

 mary process of consolidation cannot long go on in any 

 aggregate, without bringing sundry groups of units into 

 dissimilar relations to adjacent groups ; nor can it long go on 

 without subjecting each group, thus differentiated, to a pre- 

 dominant force exerted by the totality of the companion- 

 groups. Hence the change from indefinite incoherent homo- 

 geneity to definite coherent heterogeneity must accompany 

 the integration of matter ; and no alternative conclusion can 

 be reached without denying the persistence of force. 



I am aware that scanty justice is here done to the argu- 

 ments by which, in three interesting chapters, Mr. Spencer 

 establishes this deductive conclusion. But since the brief 

 exposition here given is not intended as a substitute for the 

 study of Mr. Spencer's treatise, but rather as a commentary 

 upon it, his position has been perhaps sufficiently indicated. 



We are now prepared to study with profit some of the 

 phenomena presented by the past history of our planetary 

 system. In the evolution of the sun, with his attendant 

 planets and satellites, from a vast primeval mass of vapour, 

 we shall be called upon to witness a grand illustration not 

 only of that integration of matter and concomitant dissipation 

 of motion which is the fundamental characteristic of Evo- 

 lution in general, but also of that change from indefinite 

 and incoherent homogeneity to definite and coherent hetero- 

 geneity which is its most striking derivative feature. 



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