96 THE GYPSY MOTH APPENDIX. 



amount of fluid present. From the anterior stomach the 

 food passes backward into the posterior stomach (the 

 stomach proper), an organ well supplied with strong an- 

 nular muscle fibres. In this organ the disintegration and 

 digestion of the food become more marked. By the action 

 of the stomach muscles the food is gradually forced along 

 until it reaches the narrow intestine, through which it passes 

 to the rectum, from which the refuse material is voided from 

 time to time. 



Microscopic examinations of the contents of different 

 parts of the alimentary canal show that the greater part 

 of the food retains much of its original physical character. 

 The fibrous elements pass through the system practically 

 unchanged. The softer tissues undergo a partial disintegra- 

 tion, but in general the cellular structure can be recognized. 



O 



In the contents of the cells, however, there is a great 

 change ; in food removed from the anterior stomach the cell 

 contents showed only a partial destruction, while in samples 

 from near the intestine the protoplasm had nearly disap- 

 peared, only the chlorophyll granules remaining. From 

 these examinations it appears that the process of digestion in 

 this larva is practically one of solution or extraction : the 

 digestive fluids dissolve the soluble proteids, carbohydrates, 

 fats, salts, etc., while the insoluble parts are eventually 

 ejected. The stomach muscles do not perform the function 

 of grinding, otherwise the physical characters of the food 

 would be destroyed before it reached the intestine. Doubt- 

 less the function of these muscles is to force the stomach 

 contents posteriorly, and by this movement bring the food 

 more thoroughly in contact with the digestive fluids ; the 

 same is probably true of the weaker muscles of the anterior 

 stomach, although these muscles are equally capable of 

 reverse peristalsis, as shown by the ejection of a part of the 

 contents of this organ from the mouth of the larva when- 

 ever the insect is roughly handled. 



According to Plateau, the products of digestion in herbiv- 

 orous insects consist of salts in solution, peptones, sugar 

 and emulsified fats. These substances pass by osmosis 

 through the walls of the alimentary canal and mingle with 

 the blood. 



