590 APPENDIX. 



are made similar in the highest forms of both by each having 

 a central propelling organ a heart. Now in these and in some 

 cases which the external organs furnish, such as the remark- 

 able resemblance Evolution has produced between the eyes 

 of the highest Mollusca and those of the Vertebrata, it may 

 be said that there is implied a change towards homogeneity. 

 No zoologist, however, would admit that these facts really 

 conflict with the general law of Organic Evolution. As al- 

 ready explained, the tendency to progress from homogeneity 

 to heterogeneity is not intrinsic but extrinsic. Structures 

 become unlike in consequence of unlike exposures to incident 

 forces. This is so with organisms as wholes, which, as they 

 multiply and spread, are ever falling into new sets of condi- 

 tions; and it is so with the parts of each organism. These 

 pass from primitive likeness into unlikeness, as fast as the 

 mode of life places them in different relations to actions 

 primarily external and secondarily internal; and with each 

 successive change in mode of life new unlikenesses are super- 

 posed. One of the implications is that if in organisms other- 

 wise different, there arise like sets of conditions to which cer- 

 tain parts are subject, such parts will tend towards likeness; 

 and this is what happens with their nervous and vascular sys- 

 tems. Duly to co-ordinate the actions of all parts of an active 

 organism, there requires a controlling apparatus; and the con- 

 ditions to be fulfilled for perfect co-ordination, are conditions 

 common to all active organisms. Hence, in proportion as ful- 

 filment approaches completeness in the highest organisms, 

 however otherwise unlike their types are, this apparatus ac- 

 quires in all of them certain common characters especially 

 extreme centralization. Similarly with the apparatus for dis- 

 tributing nutriment. The relatively high activity accom- 

 panying superior organization, implies great waste; great 

 waste implies active circulation of blood; active circulation 

 of blood implies efficient propulsion; so that a heart becomes 

 a common need for highly evolved creatures, however other- 

 wise unlike their structures may be. Thus is it, too, with 

 societies. As they evolve there arise certain conditions to be 

 fulfilled for the maintenance of social life; and in proportion 

 as the social life becomes high, these conditions need to be 

 more effectually fulfilled. A legal code expresses one set of 

 these conditions. It formulates certain regulative principles 

 to which the conduct of citizens must conform that social 

 activities may be harmoniously carried on. And these regu- 



