INSECTS 



pharynx immediately behind the mouth, followed by a 

 narrower, tubular oesophagus (Oe), after which comes a sac- 

 like enlargement, or crop (Cr), in which the food is tem- 

 porarily stored, and finally an antechamber to the stomach, 

 named the proventriculus. The third part of the alimen- 

 tary canal, connecting the stomach with the anal opening, 

 is the intestine, usually composed of a narrow anterior 

 part, and a wide posterior part, or rectum (Rect). Muscle 

 layers surrounding the entire alimentary tube cause the 

 food to be swallowed and to be passed along from one 

 section to the next toward the rear exit. 



With the taking of the food into the alimentary canal, 

 the matter of nutrition is by no means accomplished, for 

 the animal is still confronted with the problem of getting 

 the nutrient materials into the inside of its body, where 

 alone they can be used. The alimentary tube has no 

 openings anywhere along its course into the body cavity. 

 Whatever food substances the tissues of the animal receive, 

 therefore, must be taken through the walls of the tube in 

 which they are inclosed, ahd this transposition is accom- 

 plished by dissolving them in a liquid. Most of the nutri- 

 ent materials in the raw food matter, however, are not 

 soluble in ordinary liquids; they must be changed chem- 

 ically into a form that will dissolve. The process of get- 

 ting the nutrient parts of the raw foodstuff into solution 

 constitutes digestion. 



The digestive liquids in insects are furnished mostly 

 by the stomach walls or the walls of tubular glands that 

 open into the stomach, but the secretion of a pair of large 

 glands, called the sa/ivarv glands (Fig. 68, SIGl), which 

 open between the mouth parts, perhaps has in some 

 cases a digestive action on the food as it is taken into the 

 mouth. 



Digestion is a purely chemical process, but it must be 

 a rapid one. Consequently the digestive juices contain 

 not only substances that will transform the food materials 

 into soluble compounds, but other substances that will 



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