PREFACE 



only one natural factor is allowed to be operative at the 

 same time, he is in a position to observe correctly, after 

 repeated experiments, just what effects proceed from this 

 cause and what from that. 



Nature study, in the superficial sense, may be enter- 

 taining. We of the present age, however, must learn to 

 take a deeper insight into the lives of the other living 

 things about us. Insects, for example, are not curiosities; 

 they are creatures in common with ourselves bound by 

 the laws of the physical universe, which laws decree that 

 everything alive must live by observing the same ele- 

 mental principles that make life possible. It is only in 

 the ways and means by which we comply with the condi- 

 tions laid down by physical nature that we differ. 



Many sincere people find it difficult to believe in evolu- 

 tion. Their difficulty arises largely from the fact that 

 they look to the differences in structure between the 

 diverse types of living things and do not see the unity in 

 function that underlies all physical forms of life. Conse- 

 quently they do not understand that evolution means the 

 progressive structural divergence of the various life forms 

 from one another, resulting from the different ways that 

 each has adopted and perfected for accomplishing the 

 same ends. Man and the insects represent the extremi- 

 ties of two most divergent lines of animal evolution, and 

 by reason of the very disparity in structure between us the 

 bond of unity in function becomes all the more apparent. 

 A study of insects, therefore, will help us the better to 

 understand ourselves in so far as it helps us to grasp the 

 fundamental principles of life. 



Some writers seem to think that the sole purpose of 

 writing is that it shall be read. Just as reasonable would 

 it be to claim that the only purpose of food is that 

 it shall be eaten. In the following chapters the reader 

 is offered an entomological menu in which the consider- 

 ation of nutrient value and the requirements of a balanced 

 meal have been given first attention. As a concession to 



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