THE LAW OF EVOLUTION 



the factors which concur in the process of evo- 

 lution is complete. 



We are now prepared to show inductively 

 that wherever, as in organic aggregates, the con- 

 ditions permit, the integration of matter and con- 

 comitant dissipation of motion, which primarily 

 constitutes Evolution, is attended by a continuous 

 change from indefinite, incoherent homogeneity to 

 definite, coherent heterogeneity of structure and 

 function, through successive differentiations and in- 

 tegrations. In illustration of this statement, let 

 us describe first some of the differentiations, 

 and secondly some of the integrations, which 

 successively occur during the development of 

 an individual organism. 



Two centuries ago the researches of Harvey 

 on generation established the truth that every 

 animal at the outset consists simply of a struc- 

 tureless and homogeneous germ. Whether this 

 germ is detached from the parent organism at 

 each generation, as in all the higher animals, or 

 only at intervals of several generations, as for 

 example, in the Aphides or plant-lice, matters 

 not to the general argument. In every case the 

 primitive state of an animal is a state of relative 

 homogeneity. The fertilized ovum of a lion, 

 for instance, possesses at first no obvious char- 

 acteristic whereby it can be distinguished from 

 the fertilized ovum of a man, a dog, a parrot, 

 or a tortoise. Each part of the germ-cell is, 

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