INTRODUCTION. 



13 



tubes, which are -well represented in fig. 16. These tubes, or trachea?, 

 ramify throughout the whole of the body ; and the air passes into 

 them by means of special open- 

 ings known as spiracles, which 

 are situated alongside the body 

 of the creature. These spiracles 

 are somewhat complicated open- 

 ings, inasmuch as they open to 

 receive air, shut to maintain a 

 supply, and again open for ex- 

 pulsion. The act of breathing, 

 therefore, is somewhat after the 

 nature of a bellows, inasmuch as 

 air is received at a special open- 

 ing and driven throughout the 

 tubes. In addition to the func- 

 tion of breathing, it is obvious 

 that the inflating of the tubes 

 is associated with the machinery 

 of flight. Fig. 17 is a photo- 

 graphic representation of a 

 trachea from a butterfly. 



The organs concerned with 

 feeding and digestion occupy a 

 considerable space in the body- 

 cavity of many insects. From 

 actual specimens this can only 

 be understood by careful dis- 

 section and microscopical man- 

 ipulation. The accompanying 

 figure, however (fig. 18), taken 

 from Miall and Denny, will con- 

 vey a very good idea of these 

 internal organs. 



In the centre of the figure 

 the food - canal is represented. 

 At s we have the salivary glands and reservoir which contain the 

 saliva, which is not only beneficial in digesting the food within 



Fig. 16. Diagram of the ch ief tru nks of the tracheal 

 system of an, insect ; the central nervous system is 

 also shown. 



a, antenna? ; o, eye ; st', anterior stigma ; I, longi- 

 tudinal trunk. After Kolbe. (From ' Text- 

 Book of Zoology,' by Dr J. E. V. Boas.) 



the canal. 



but in some sucking 



insects is mixed with the crude 



