CHAPTER II 



FEEDING AND BREATHING 



The diverse systems of organs that build up the body of 

 any animal and the various functions that these perform 

 are so closely inter-related with one another, that it is 

 impossible to consider any one system or mode of activity 

 entirely by itself. Yet for a detailed discussion of the 

 biology or " life-knowledge " of a creature, it is necessary 

 to attempt, in some kind of order, a survey of its various 

 organs and their actions, though opinions may well differ 

 as to what order is the most convenient and reasonable. 

 In this discussion of the Biology of Insects it is proposed 

 to begin with the functions of feeding and breathing and the 

 important series of changes within the body associated with 

 these familiar manifestations of life. 



All observers of nature have in mind a distinction, 

 implied if not expressed, between living creatures and life- 

 less objects. In this book it is assumed that such distinction 

 is justified, and while questions about the ultimate meaning 

 of life must be left to the philosopher, the visible manifesta- 

 tions of life — the modes of behaviour of living creatures — 

 are proper subjects of study for the naturalist. Among 

 these, feeding is one of the most obvious, as well as one of 

 great importance. In our introduction (p. lo above) we 

 have noticed that not the whole body of an insect is alive ; 

 we have dwelt, for example, on the distinction between the 

 outer cuticle or exoskeleton, which is a horny, lifeless 

 envelope, and the skin, a sheet of living cells beneath, by 

 whose activity the cuticle is built up (Fig. i). 



The essential component of these cells, the substance 



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