CHAPTER III. 

 THE VITAL PROCESSES. 



Respiration. 



In insects, as in all animals, a renewed supply of 

 oxygen is necessary to supply the energy used up in all 

 the forms of bodily activity, as well as to analyze the food 

 into tissue-building products. But insects have no 

 lungs, nor any suggestion of an oxygenating center 

 communicating with a blood center where the oxygenation 

 of the food-laden blood is accomplished. Neither does 

 the air enter the insect's body through an opening in the 

 head. Indeed, the respiratory system of an insect is 

 rather a sack closed at the head end. The respiratory 

 system of an insect is much more complex than that of 

 human beings. It consists of a system of air tubes 

 much resembling the windpipe of a bird, but branching 

 so many times as to become delicate enough to carry 

 the air directly to the finest subdivision of any tissue of 

 the insect's body, going in between the eye elements, 

 driving their load of air inside the wing sacks, in between 

 the leg muscles, even down to the delicate tarsal and 

 antennal segments. It is thought by some histologists 

 that the ultimately fine tracheal tubes may enter a cell 

 itself and oxygenate the protoplasm. 



On account of the usual rigidity of the head and the 

 thoracic segments, the respiratory movements can hardly 

 be noticed in these parts of the body of most insects. 

 But the abdominal segments move much more freely 



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