DIGESTION. 95 



has been known to devour bark, buds, blossoms and fruit, 

 but, as these are exceptions, they may be properly excluded 

 from consideration. 



Leaves may be said to consist of a large amount of organic 

 matter associated with water, and a small quantity of mineral 

 matter. In the ash are found certain elements, such as pot- 

 ash, lime, phosphorus, etc., which play an important role 

 in plant economy ; but the substances serving as food in 

 leaves are organic, and consist mainly of proteids, carbohy- 

 drates and fat. These compounds are present in the proto- 

 plasm with which the cells are filled, and, w r hen consumed and 

 assimilated by the insect, serve as muscle builders, sources 

 of fat, energy and heat, repair wasted tissues and bring 

 about the normal growth of the insect. Undoubtedly the 



*_. * 



proteids are the most important food elements, and probably 

 serve as the source of the chitin of which the body integu- 

 ment is formed. The lignin, cellulose and similar substances 

 found in leaves are of but little value as food. 



THE DIGESTIVE SYSTEM. 



The internal .anatomy of the larva, pupa and imago has 

 been fully detailed in another place,* hence it will suffice to 

 state that the digestive system of the larva consists of a pair 

 of stout jaws, a buccal cavity, a pharynx dilating into an 

 anterior stomach in the forward body segments, a stomach 

 proper, extending through a greater part of the body cavity, 

 an intestine and a short dilated rectum. Discharging into 

 the mouth are a pair of salivary glands, while six malpighian 

 vessels are attached to the rectum. 



THE DIGESTIVE PROCESSES. 



The jaws of the larva serve to incise and comminute the 

 food which passes directly from the mouth into the anterior 

 stomach, where it is subjected to the action of an alkaline 

 fluid. It is of interest to note that in this stomach, some- 

 times greatly distended with food, there is always a large 



* Kirkland, article on "Internal Anatomy;" "The Gypsy Moth," Forbush- 

 Fernald, 1896. 



