6.' Appendages of the Thorax. 



APPENDAGES OF THE THORAX. 



The organs of flight are the most noticeable appendages 

 of the thorax. The wings are usually four, though the 

 Diptera have but two, and some insects — as the worker- 

 ants — have none. The front or pi'imary wings (Fig. 4, 

 A) are usually larger than the secondary or hind wings 

 (Fig. 4, B'), and thus the mesothoracic or middle ring of 

 the thorax, to which they are attached, is usually larger 

 than the metathorax or third ring. The wings consist of 

 a broad frame-work of veins (Fig. 4), covered by a thin, 

 tough membrane. The main ribs or veins are variable in 



Fig. 15. 



Muscles oj Thorax, ajter Wolff, 



L Muscles to raise front wing. D Muscles to lower front wine. 



A Muscles of hind wing. 



number, while towards the extremity of the wing are more 

 or less cross-veins, dividing this portion of the wings into 

 more or less cells. In the higher groups these cells are 

 few, and quite important in classifying. Especially useful 

 in grouping bees into their faimilies and genera, are the 

 cells in the second row, from the front or costal edge of 

 the primary wings, called the sub-costal cells. Thus in the 

 genus Apis there are three such cells (Fig. 4, A, 6, 7, 8), 

 while in the Mclipona there are only two. The ribs or 

 veins consist of a tube within a tube, the inner one form- 

 ing an air tube, the outer one carrying blood. On the costal 



