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 entertaining. 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 elemental principles that make life possible. It is only in the ways and means by which we comply with the conditions laid down by physical nature that we differ.
Many sincere people find it difficult to believe in evolution. 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. Consequently 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 extremities 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 consideration of nutrient value and the requirements of a balanced meal have been given first attention. As a concession to
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