191S] Alimentary Canal of Altica Larva 291 



THE (ESOPHAGEAL VALVE. 



In typical cases among insects, such as Pieris or Simulium, 

 the oesophageal valve is a large fold of the fore-intestine, which pro- 

 jects down into the mid-intestine, almost closing the aperture be- 

 tween them. The function assigned to it is that of preventing 

 the regurgitation of food, due to the peristaltic movements of 

 the intestine. 



In Aliica bimarginata there is a fold of the fore-intestine 

 which projects slightly down into the mid-intestine, and marks 

 the point of transition between these two regions. It is by no 

 means large enough to close the lumen and can be of but little 

 if any use as a means of preventing the repassing of food into 

 the fore-intestine. However, there is a strong constriction 

 between the crop and the ventriculus, and the opening between 

 the two is much less than the diameter of the alimentary canal 

 at this point, so an oesophageal valve is little needed, and this 

 fold is probably all that is necessary. In its structure the 

 oesophageal valve is much like the rest of the crop. Intima, 

 epithelium and basement membrane are clearly distinguishable. 

 The primary intima becomes very thin, but distinction between 

 primary and secondary intima continues to the end. This con- 

 dition is very similar to that described byPoyarkoff (l<)l()j in 

 the elm leaf beetle. 



The oesophageal valve of Altica bimarginata is shown in 

 figure '.). 



THE TRANSITION BETWEEN THE FOKE-INTESTINE AND THE 



MID-INTESTINE. 



Intima. The intima disappears at the end of the fore- 

 intestine. 



Striated border. A striated border is developed on the inner 

 face of the cells in place of an intima throughout the mid- 

 intestine. 



Epithelium. There is a well marked transition between the 

 type of epithelium characteristic of the fore-intestine and that 

 characteristic of the mid-intestine, even though there is no sud- 

 den change. The cells of the fore-intestine at the posterior face 

 of the oesophageal valve become first cuboidal, and then nar- 



