Seventeen-year Locust. 135 



because there is occasion for performing the most 

 important acts only once in a hfetime, and that too 

 under such conditions as to make it impossible that 

 the actors should learn from others. In such cases 

 we find Instinct ever ready to do its work — a work 

 sometimes so complex as to require careful study 

 on the part of man to understand it. This point 

 can perhaps be made plain by a single illustration. 

 The Cicada or Seventeen-year Locust is so called 

 because it appears only once in seventeen years. 

 The insects deposit their eggs in the limbs of trees 

 and die. The young grubs find their way to the 

 earth and there mine in the dark for seventeen 

 years, when they come forth for their few days of 

 life in the sunlight. When they come out they 

 are to deposit their eggs and do all the work which 

 their ancestors did seventeen years before. They 

 do the work but once in a lifetime, but every move- 

 ment goes on in perfect order, as though experience 

 and instruction both had done their perfect work 

 on beings capable of comprehension. They copy 

 exactly the work done by their ancestors seventeen 

 years before, when they themselves existed only in 

 the eggs. 



We have thus far found Instinct as meeting the 

 demands of appetite — as protecting its possessor 

 from special enemies, and as taking its place, with 

 color and form and function, as a higher agency for 

 preserving the hfe of the individual and the species. 

 We have found nothing yet to indicate that it is an 

 entity, a thing by itself, as it is often represented to 

 be, — a possession which animals have in common. 



