INSECTS 



what tells the creature that liberty is to be found above, 

 and not horizontally or downward? Many people believe 

 that these questions are not to be answered by human 

 knowledge, but the scientist has faith in the ultimate solu- 

 tion of all problems, at least in terms of the elemental 

 forces that control the activities of the universe. 



We know that all the activities of animals depend upon 

 the nervous system, within which a form of energy resides 

 that is delicately responsive to external influences. Any 

 kind of energy harnessed to a physical mechanism will 

 produce results depending on the con- 

 struction of the mechanism. So the ef- 

 fects of the nerve force within a living 

 animal are determined by the physical 

 structure of the animal. An instinctive 

 action, then, is the expression of nerve 

 energy working in a particular kind of 

 machine. It would involve a digression 

 too long to explain here the modern con- 

 ception of the nature of instinct; it is 

 sufficient to say that something in the 

 surroundings encountered by the newly- 

 hatched grasshopper, or some substance 

 generated within it, sets its nerve energy 

 into action, that the nerve energy work- 

 ing on a definite mechanism produces the 

 motions of the insect, and that the 

 mechanism is of such a nature that it 

 works against the pull of gravity. Hence 

 the creature, if normal and healthy in all 

 respects, and if the obstacles are not too 

 great, arrives at the surface of the ground 

 as inevitably as a submerged cork comes 

 to the surface of the water. Some 

 readers will object that an idea like this destroys the 

 romance of life, but whoever wants romance must go to 

 the fiction writers; and even romance is not good fiction 



Fig. 7. Eggs of a 

 species of katydid at- 

 tached to a twig; the 

 young insect in suc- 

 cessive stages of emerg- 

 ing from an egg; and 

 the newly-hatched 

 young 



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