132 



proventriculus to the origin of the malpighian 

 tubes. It consists of two portions which merge 

 into one another — an anterior narrow portion, 

 and a large dilated posterior portion, which 

 becomes greatly distended after feeding. Unlike 

 most insects there are no caecal appendages in 

 the mosquito. Posteriorly there is a marked con- 

 striction, with strong muscular bundles, which 

 forms a very marked pylorus (Fig. 30). 



The anterior narrow portion of the mid-gut 

 lies in the thorax, and does not become distended 

 with blood. The posterior portion when fully 

 dilated fills the greater portion of the abdomen, 

 the viscera being pushed into the last few segments. 



The Hind-gut. — The hind-gut is short and 

 passes in one or two bends from the pylorus to 

 the anus. Immediately beyond the pylorus there 

 is a considerable dilatation which is poorly sup- 

 plied with muscular fibres : into this open the 

 five malpighian tubules. For a short distance 

 beyond this the lumen is narrow (small intestine), 

 but becomes gradually larger (colon). At the 

 termination of the colon there is a shght constric- 

 tion, after which the canal dilates again to form 

 the rectum (Fig. 30). 



Into the rectum project six solid growths, 

 the so-called rectal glands, which are, however, 

 papillae. Posteriorly the rectum ends in the anus 

 close above the gynaephoric canal. 



The appendages of the alimentary canal 

 are : — 



The Salivary Glands. — The salivary glands 

 consist of six tubular acini lying three upon either 

 side. Those of one side lie generally one above 

 the other in the long axis of the body, their 



