INTERNAL ORGANS. 81 



inent longitudinal ridges ; while the posterior 

 half, or colon, is smoother and less muscular 

 within [Fig. 78]. 



The anterior appendages to the intestinal canal 

 are a pair of salivary glands, little white threads 

 having their origin near the commencement of the 

 oesophagus, and running along this nearly to 

 the stomach. The posterior appendages are a 

 pair of malpighian vessels, also composed of ex- 

 ceedingly long slender threads ; they originate on 

 each side of the intestine, and Very soon subdivide 

 into three tortuous branches, which pass forward 

 and backward along the walls of the stomach, and 

 linally, returning to the point from which they 

 started, cover the intestine with a most intricate 

 mass of convoluted threads. 



The respiratory system consists of a series of 

 air- tubes ramifying indefinitely, each set of which 

 originates in a single trunk, opening from one of 

 the numerous spiracles or breathing pores with 

 which we have found the insect provided ; close 

 to the origin of this trunk a large air-canal runs 

 along the sides of the body, connecting all the 

 trunks of one side, while other shoots originate 

 from the canal itself ; and, indeed, as it passes 

 through the second and third thoracic segments, 

 which, as already stated, possess no spiracles, 

 this canal emits large branching trunks just like 

 those of the other segments, directly opposite the 



