66 



Mosquitoes 



he does not wonder that the little wretches can 

 wiggle so fast. The alimentary canal begins with 

 the esophagus, a short, straight tube extending from 

 the mouth to the stomach. The latter is a dilated, 

 straight pipe in the median line, varying in appear- 

 ance according to its contents. It begins in the 

 upper part of the thorax, and extends to the sixth 

 abdominal segment, where it narrows and continues 



as the rectum. In the 

 living larva there will be 

 perceived in the thorax 

 four pairs of dark spots, 

 more or less variable. 

 These, at first, may appear 

 like pigmentation, but on 

 inspection will be found 

 to be within the skin. 

 They are glandular sacs, 

 probably having the function of the "liver," and are 

 connected by ducts with the upper end of the stom- 

 ach. At the beginning of the rectum are the five 

 Malpighian tubes. Above the stomach, one on each 

 side of the middle line, will be seen the great 

 tracheae, which expand more or less in the thoracic 

 portion and in the breathing tube, and are easily 

 distinguished by their walls of spirally coiled threads 

 of chitin. From these main tracheae small branches 

 extend to the different organs of the body. The 

 blood, which flows freely about in the body cavity, 

 is clear, colourless, and has no oxygen-carrying cells, 

 but is more in the nature of lymph. It is kept in 

 circulation by the " heart," a dorsal tube, open at 



Fig. 12. — Labium of Och- 

 lerotatus sollicitans larva, dorsal 

 side, greatly enlarged. 



