INSECTA 



443 



certain regions of the nervous system which exercise a controlHng 

 influence over the respiratory activity of the insect as a whole. One 

 example will serve to illustrate this point. The nymph of the dragon- 

 fly Libellula pumps water for respiratory purposes into its rectum. 

 In the natural state it responds to changes in oxygen content of water 



Fig. 310. Diagrams to illustrate the theory of tracheal respiration. A, Trache- 

 ole ending in resting muscle; B, In active muscle, i, trachea; 2, tracheole 

 cell; 3, parts of tracheoles containing air; 4, parts of tracheoles containing 

 liquid; 5, muscle. After Wigglesworth. 



quite readily, by increasing the rate of its respiratory movements, 

 when there is oxygen lack ; reducing such movements in water satur- 

 ated with oxygen. When however the prothoracic ganglion is de- 

 stroyed, respiratory movements continue evenly, without reference 

 to the oxygen tension of the water. 



