208 THE BIOLOGY OF THE SEASONS 



of the inexorability of inheritance ; but we can, by judicious 

 changes in surroundings and habits, modify the individual 

 very much for the better, especially if we begin early 

 enough. 



If we are to think clearly of modinability, we must 

 distinguish not only between inborn variations and acquired 

 modifications, but between direct modifications and the 

 secondary results of these, i.e. between direct modifications 

 and those changes to which the environmental change was 

 only the liberating stimulus pulling the trigger that 

 allowed a latent character to find expression. We must 

 also admit the possibility the discovery of which is one of 

 the most progressive steps in modern evolutionistic experi- 

 ment that an environmental change may affect the next 

 generation without affecting the present one. Professor 

 Tower of Chicago worked for a dozen years on beetles of 

 the genus Leptinotarsa, which he subjected to unusual 

 conditions of temperature and moisture when the male or 

 female reproductive organs were at a certain stage in 

 their development. The result was to induce in the 

 offspring striking changes in colour and markings, and 

 also in some details of structure. Sometimes all the germ- 

 cells seemed to be affected, sometimes only a fraction of 

 them ; sometimes various changes resulted from the 

 same treatment ; some of the changes were brusque, 

 others showed intergrades with the parental conditions ; 

 sometimes the changes did not occur until after the lapse 

 of several generations in the unusual environment. It is 

 obvious, of course, that the experimenter could only 

 influence the reproductive cells through the body of the 

 parent, but the important point is that the body of the 

 parent was not affected. Here, in other words, we have 

 definite evidence of germinal variation evoked by environ- 

 mental stimulus. 



