358 THE BIOLOGY OF INSECTS 



and endows it with a size and power which it does not 

 possess in animals which exercise it less." The opposite 

 result is also assumed : ** The permanent disuse of an 

 organ, arising from a change of habits, causes a gradual 

 shrinkage and ultimately the disappearance and even 

 extinction of that organ." And the modification thus 

 acquired is believed to be transmitted to the race : *' All the 

 acquisitions and losses wrought by nature on individuals 

 . . . are preserved by reproduction to the new individuals 

 wliich arise." Among the examples cited by de Lamarck 

 in support of his theory are '' many insects," which, 

 although they '* should have wings according to the natural 

 characteristics of their order . . . are more or less com- 

 pletely devoid of them through disuse." This is a sug- 

 gestive illustration in view of the discussion earlier in this 

 chapter (p. 346) on the origin of the wings of insects, for 

 if use-inheritance really works it might have been a factor 

 in elaborating these organs from some primitive rudiments 

 which at first were less than wings. Use-inheritance as a 

 factor of evolution has appealed to the imagination of 

 multitudes and was accepted as a true cause by many 

 naturalists of the nineteenth century, though they did not 

 follow de Lamarck in regarding it as the most important 

 agent in the evolutionary process. Because the effects of 

 use and disuse of organs and faculties are often unmistakably 

 apparent in the individual, it seems natural to conclude that 

 they must also be exhibited in the history of the race. Many 

 are thus ready to believe that among insects, the possession 

 of ample wings follows from strenuous efforts to fly on the 

 part of far-off ancestors, or that the blind beetles and spring- 

 tails characteristic of a modern cave-fauna have lost the power 

 of sight on account of the unknown number of past genera- 

 tions that dwelt in darkness. Such explanations involve 

 the view that modifications during the lifetime of the 

 individual through environment, activity, or inaction, tend 

 to become congenital so that their effect can be traced, at 

 least to some extent, in succeeding generations. This 

 theory of " acquired changes " which become hereditary 



