SKETCH OF CLEMEN CE ROYER. 693 



set to Nature. Atavism is the constant quantity, and the force of 

 variation is the perpetually changing unknown factor. The prob- 

 lem is therefore complex, but the principles to which the variable is 

 subject resolve themselves into a series of partial laws which are de- 

 duced from an aggregate of observations, and which, according to 

 our author, one may summarize as he goes. 



Most of the variations reveal themselves in the embryo during the 

 fsetal period. But after its birth the young product is affected not 

 only by the ambient medium, but also by the consequences of the 

 reproductive act. The latter, in fact, having impressed the initial 

 movement upon its organism, reacts incessantly against the modify- 

 ing influences of the ambient, and atavism prevails as always the 

 resultant unless important accidents come in to change the course. 



It is only necessary to add a few experimental considerations to 

 complete a rapid sketch of the laws of variability. First, correlation 

 of growth: Homologous organs tend to vary in the same direction, 

 and together. Are the fingers joined or divided? The hand follows 

 similar variations. Then there is a compensation of growth which 

 prevents the excess of the preceding rule; when one organ is de- 

 veloped, another is atrophied. Also vital competition. Every or- 

 ganized being must be in harmony with the conditions of its existence 

 or it will not subsist; the monster may appear, but will not live. 

 Lastly, by virtue of natural selection, the individual must likewise 

 possess the means of perpetuating its species. Otherwise, a series of 

 transformations will come to pass in the course of successive genera- 

 tions, improving the organism and adapting it more and more to the 

 exigencies of its habitat. The least prolific species of to-day fulfill 

 these conditions so well that they of themselves alone would cover the 

 surface of the earth if their multiplication was not checked by that 

 of other species. But as only a limited quantity of life is possible on 

 our planet, the less well-adapted organisms perish. The struggle 

 therefore produces a selection. It is hence presumed that in the same 

 species only varieties manifesting tendencies in most complete har- 

 mony with the method of their existence will be preserved, all 

 the intermediate varieties being destroyed. Consequently, if we 

 push the doctrine of Darwin to its extreme limits, we arrive at the 

 idea, now rejected, that in the beginning only a single germ arose at 

 one point on the globe. All the analogies, on the other hand, lead us 

 to suppose that the earth was fruitful over its entire surface. 



This leads us to inquire how life appeared on the earth. The de- 

 bate between the heterogenists and the panspermists has been long 

 vain, because the question has been laid before them in insoluble terms. 

 In order to resolve it, therefore, we must take ourselves back in 

 thought thousands of thousands of centuries in the past. A thin crust 



