196 EVOLUTION 



v 



propounded a generation ago much the same 

 doctrine of ;< Organic Memory," as that 

 which we now owe to Semon. Haeckel too 

 has expounded much the same doctrine; 

 and no doubt in increasingly clarified form it 

 must henceforth be reckoned with. 



(5) Insensibly, again for it is all a matter 

 of degree we pass from the temporary dints 

 impressed upon the organism by the environ- 

 ment to those that last. There are many 

 cases in which the novel conditions provoke 

 a structural change from which there can be 

 no rebound, the limit of organic elasticity 

 having been passed. These lasting changes 

 are technically called '* modifications ' or 

 ;< acquired characters." A tree may be per- 

 manently blown out of shape; over-exertion 

 at high altitude may strain the heart beyond 

 repair; a man may be tanned for life by the 

 tropical sun. 



(6) Quite different from the last are cases 

 where some change in the environment of 

 the parent provokes a variation in the off- 

 spring. The best instances, as yet, are to be 

 found in the experiments carried on for many 

 years by Tower on beetles of the genus 

 Leptinotarsa, which he subjected to unusual 

 conditions of temperature and humidity, 

 when the male and female reproductive 

 organs of the parent were at a certain stage 



