98 THE LESSON OF EVOLUTION 



which is founded on this analogy, and which I confess 

 I find hard to follow. If I understand his argument 

 rightly, it is this. He commences by saying that, 

 during the development of every individual there are 

 one or more periods when development is more rapid 

 than at other times. He then makes the statement 

 that if reproduction takes place during one of the 

 rapid periods of development, the offspring will be 

 highly variable ; but if reproduction takes place 

 during one of the slow periods of development, then 

 the offspring will not be variable. And, finally, he 

 declares that it is the same with a genus as with an 

 individual. The genus also has periods of rapid 

 change, and periods of persistency ; and species 

 originating when the genus is undergoing rapid change 

 will be variable, while those originating during periods 

 of persistency will be constant. 



Even if there were facts to support the statements 

 that offspring will be variable or not, according as they 

 are born at stated periods of life ; that genera shew 

 periods of rapid change and of persistency ; and that 

 species diverging at those periods are themselves 

 variable or persistent even if all these points could 

 be established, the reasoning from analogy seems to 

 me very feeble, and hardly to require refutation ; for 

 the two classes of facts are not in any way connected. 



Mr A. Smith Woodward also thinks that the evolu- 

 tion of animals shews a rhythm. He supposes that 

 the development of every group has two phases. (1) 

 A new type hides away, as it were, in some other 

 district than that in which it originated ; but it has 

 great developmental energy, and finally spreads over 

 every habitable region, displacing the effete race from 



