LIFE; BODY AND MIND 209 



rhythms, such as the seasonal or daily changes 

 in plants and animals. A creature that has long 

 been responding to daily changes of light and 

 darkness will continue to show these daily varia- 

 tions for some time after it is placed in a room 

 of constant illumination; but if subjected to a 

 new period of alternation, a new adjustment 

 finally comes whereby the creature has adapted 

 himself to his new circumstances. It is such 

 adaptations that show how far even the simplest 

 organisms are removed from mere mechanisms. 

 Then the book goes on to deal with the instincts 

 which are so extremely characteristic of the 

 insect world — instincts so nearly immutable 

 that they persist through geological epochs, 

 and yet not altogether immutable. The insect 

 often shows its power to invent or learn new 

 methods ; and when we see the mass of evidence 

 that Bouvier has brought forward it is hard to 

 doubt his conclusion that this learning is in 

 some measure transmitted to posterity. 



For example, an insect accustomed to eating 

 the leaves of a certain plant is forced with great 

 reluctance to eat the leaves of a different plant ; 

 but after two or three generations the insect not 

 only prefers the new food, but even, having an 

 option, lays its eggs upon the new plant. This 



