INSECTS 



The environmental conditions of the life of cells in a 

 complex animal are too complicated for an elemental 

 study; the elements of life and its basic necessities are bet- 

 ter understood in a simple organism, or in a one-celled 

 animal; but for purposes of description, it is most con- 

 venient to speak of the properties of mere protoplasm. 

 All the vital needs of the most highly organized animal are 

 present in any part of the protoplasmic substance of which 

 it is composed. 



Protoplasm is a chemical substance, or group of sub- 

 stances, the structure of which is very complex but is main- 

 tained so long as there is no disturbance in the environ- 



,GCls 



Fig. 62. Diagram showing the relation of the germ cells iGCls) and the body 



cells (BCls) in successive generations 



A fertilized germ cell of generation A forms the germ cells and body cells of B, 



a fertilized germ cell of B forms the germ cells and body cells of C, and so on . 



The offspring C of B derives nothing from the body cells of the parent B, but 



both offspring C and parent B have a common origin in a germ cell of A 



ment. Let some least thing happen, however, such as a 

 change in the temperature, in the strength of the light, in 

 the weight of pressure, or in the chemical composition of 

 the surrounding medium, and the protoplasmic molecules, 

 in the presence of oxygen, are likely to have the balance of 

 their constituent particles upset, whereupon they partly 

 decompose by the union of their less stable elements with 

 oxygen to form simpler and more permanent compounds. 

 The decomposition of the protoplasmic substances, like all 

 processes of decomposition, liberates a certain amount of 

 energy that had been stored in the making of the molecule, 

 and this energy may manifest itself in various ways. If it 



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