38 



THE INTERNAL STRUCTURE OF MUSCA DOMESTICA 



The Proximal Intestine (j).int.) is the hmgest region of the 

 gut. It varies in length considerably. In the normal-sized con- 

 dition its course is as follows : Beginning at the anterior end of 

 the abdomen, it runs dorsally beneath the heart to the posterior 

 region, where it curves downwards, turns to the left, and runs 

 forward for a short distance, curving to the right, where it 

 doubles back transversely to the left. Here it doubles sharply 

 back to the right, from whence it runs forward for a little way 



Fig. 14. The posterior region of the alimentary canal, to show the rectal glands 

 {rect.gl.) with their tracheal supply, the origin of the malpighian tubes {nialp.), 

 and the position of the rectal valve indicated at X. 



and crosses over to the left. Curving, it runs posteriorly to 

 become the distal intestine. Its walls are lined by an epithelium 

 of large columnar cells. 



The Distal Intestine (d. int.). The junction of this with the 

 proximal intestine is marked by the entrance of the ducts of 

 the malpighian tubes. It runs posteriorly and curves dorsally 

 and forwards to becon>e the rectum, from which it is separated 

 by a cone-shaped valve, the rectal valve, the position of which 



