en. iv.] THE LAW OF EVOLUTION. 329 



have already seen to consist in the integration of matter and 

 concomitant dissipation of motion, but which, as we shall 

 presently see, implies in most cases much more than this. 

 Let us first point out the conditions under which the secon- 

 dary redistributions attending Evolution take place ; and let 

 us then proceed to point out the common characteristics of 

 these secondary changes. 



Obviously in speaking of secondary redistributions that go 

 on while a body is integrating its matter and losing its 

 motion, we refer to redistributions among the parts of the 

 body and among the relative motions of the parts, — or, in 

 other words, to alterations in structure and function going on 

 within the body. Now the ease with which such redistribu- 

 tions are effected, and the ease with which they are 

 maintained, must depend alike, though in precisely opposite 

 ways, upon the amount of motion retained by the integrating 

 body. The greater the amount of retained motion, the more 

 easily will internal redistributions be effected. The smaller 

 the amount of retained motion, the more easily will such 

 redistributions be rendered permanent. These propositions 

 are so abstruse as to require some further illustration. 



When water is converted, by loss of its internal motion, 

 into ice, the amount of secondary rearrangement which 

 occurs among its particles is comparatively slight, but it is 

 permanent so long as the state of integration lasts. During 

 the continuance of the solid state there is not enough 

 mobility among the particles to admit of further rearrange- 

 ment to any conspicuous extent. On the other hand, after 

 steam has been integrated into water, the retention of a con- 

 siderable amount of molecular motion allows internal re- 

 arrangement to go on so easily and rapidly that no momentary 

 phase of it has a chance to become permanent; and there 

 can thus be no such stable arrangement of parts as we call 

 structure. The phenomena of crystallization supply us with 

 kindred, but slightly different examples. When a crystal is 



