54 HUMBLE CBEATTJEES. 



situated on the thorax, and a pair upon each ring of 

 the abdomen. 



In the common Housefly, these spiracles are very 

 beautifully formed, the entrance being partially closed 

 by a great number of ramifications of the external 

 covering of the body, proceeding from the circum- 

 ference of the spiracle, and forming a delicate net- 

 work, the object of which is to prevent particles of 

 dust from entering along with the atmosphere. In 

 the Bee, however, the contrivance is of a different 

 kind, consisting of two elongated apertures, one be- 

 hind the other (PL VII. fig. 3), and the outer one 

 only provided with a number of short hairs for the 

 purpose of precluding foreign substances, instead of 

 the beautiful ramifications that are present in the 

 Housefly. 



Through these spiracles or breathing-holes, then, the 

 air is admitted into special organs which enable it to 

 circulate through the body (PI. VII. fig. 2, «a'6,&c.*), 

 and consisting of a number of sacs or bladders that 

 communicate with one another, and with the external 

 atmosphere, by means of wonderfully constructed 

 tubes, called tracheoe. 



The distribution of these sacs and tubes is de- 

 serving of especial attention, and we must ask you to 

 accompany us in an examination of the plate repre- 

 senting this portion of the insect^s anatomy (PI. VII. 

 fig. %,aa' d, and hbh, &c., the part drawn in tint). 



* The respiratory system is represented by the large sac and 

 connecting tubes at the left side of the figure. 



