236 MODERN IDEAS OF EVOLUTION 



plasm constituting the nucleus of this embryo cell. This 

 minute living speck must contain in it potentially all the 

 parts and organs that are produced from it. Weismann 

 illustrates this in a clear manner by the observed fact of the 

 spontaneous division of this nucleus into a vast number of 

 separate granules, each of which plays a part in the formation 

 of some portion of the embryo animal. 



From this simple statement it follows beyond controve 

 that any cause which effects a change in the structure 

 properties of the future individual must pre-exist in t. 

 germ, and that any effect of external causes on the adi j 

 animal can have no effect in this respect unless it has modi 

 fied the germ or germs of the new generation. 



This conclusion, to which no physiologist can reasonably 

 object, if it does not altogether subvert, as some think, the 

 Darwinian and Lamarckian doctrines of evolution, at least 

 weakens their force and diminishes their extent, and besides 

 goes quite behind them into a region of antecedent causes, 

 and shows that they must be of secondary value and im 

 portance. Weismann also insists very strongly on what he 

 calls the * immortality or properly, perpetuity of germinal 

 matter embodying the characters of the species a very 

 important and valuable idea. 



All this leads us, however, not so much to deny that any 

 causes acting on the adult can modify its progeny, as to 

 inquire what causes, if any, can so profoundly affect the 

 organism as to modify its germinal matter. 



On this question we may first remark that such causes 

 seem often to be psychical rather than material that is, causes 

 affecting the imagination and emotions. This has been 

 known at least since the time of Jacob s experiment with 

 Laban s cattle, and probably long before. It is still a matter 

 of every-day experience both in man and animals, and opens 

 a wide and inviting field of study, leading, perhaps, to more 



