94 WHAT EVOLUTION IS 



sumed to be inherited are often quite 

 different and the question, therefore, 

 of real inheritance remains open. 

 The same general criticism applies 

 to Griffith's studies on the inheritance 

 of defects in the internal ear of the 

 rat. Both these lines of investiga- 

 tion, and especially those of Guyer 

 and Smith, are, however, extremely 

 near the point and are very sugges- 

 tive. 



A novel and very remarkable test 

 of the inheritance of acquired char- 

 acters is one that has been advanced 

 by the celebrated Russian physiolo- 

 gist Pawlow. It is well known that 

 mice can be trained easily to come to 

 a particular place for food. If, dur- 

 ing this training, a bell is sounded 

 each time that the animals are fed, 

 they will learn after a while to come 

 for food at the sound of the bell even 

 when no other signal for the presence 



