GRASS THRIPS. 57 



DIGESTIVE SYSTEM AND ACCESSORY GLANDS. 



P*g /• 



The alimentary canal is small and short. It is only about one 

 and one-half times the length of the body. 



The mouth is little more than a narrow tube through which 

 the setae project. At its upper end it widens out and joins the 

 pharynx, which runs anteriorly for a short distance, then turns 

 sharply back, and joins the oesophagus. The oesophagus is very 

 narrow and has an exceedingly small lumen. It passes back- 

 ward over the anterior end of the first thoracic ganglion, and runs 

 back to the middle of the mesothorax, where it joins the mid- 

 intestine. 



The mid-intestine is the longest part of the canal. It is sep- 

 arated by three constrictions into four divisions. The first and 

 second divisions of the mid-intestines are of about equal length 

 and together they extend from the mesothorax to the fifth 

 abdominal somite, where they join the third division. At this 

 point there is a sharp turn and the third division runs anteriorly 

 as far as the anterior part of the third abdominal somite. Here, 

 again, there is another turn, and the fourth division runs pos- 

 teriorly as far as the sixth abdominal somite, where it joins the 

 hind-intestine. At this point the malpighian tubules enter the 

 intestine. 



The hind-intestine is small and somewhat convoluted. It 

 shows no division into ileum and colon. At the posterior end 

 it is enlarged to form the rectum. 



The mouth and pharynx have a chitinous lining which is quite 

 thick. The anterior part of the oesophagus also has a thin, flex- 

 ible, chitinous lining. The outer walls of the oesophagus are very 

 thin and delicate and have very few muscle fibers. 



The walls of the mid-intestine are much thicker, and are com- 

 posed of several layers. On the inside is the lining membrane, 

 the cuticula. Just outside of this, with their apices projecting 

 into the lumen of the intestine, is a layer of large pyramidal epi- 

 thelial cells. These cells are imbedded in a basement membrane 

 of connective tissue, outside of which there are two layers of 

 muscle fibers, one circular and the other longitudinal. Outside 

 of these there is a thin membranous covering. 



