30 AN INTRODUCTION TO ENTOMOLOGY. 



obtain their food. We do not know yet how generally this is true 



of sucking insects. 



Following the pharynx and extending into or through the thorax 



is a slender part, the oesophagus. 



In many insects, both sucking and biting, there is a dilation of 



the oesophagus near its caudal end, which serves as a reservoir of food, 



and is termed the crop. The crop of sucking insects was formerly 



thought to be the pumping organ, and is, therefore, described in the 



older works on this subject as the sucking stomach. 



Following the crop we find in some insects 

 a compact enlargement of the alimentary canal 

 with strong muscular walls, the proventricitlus 

 or gizzard. This is sometimes a very com- 

 plicated organ, furnished with teeth, spines, 

 and hairs, for the grinding of the food. (Fig. 



Fig. 3q. — Cross-section of 

 the proventriculus of 39") 



The stomach is next in order, and is easily 

 recognized by its central position, and usually by its large size. 

 It is also known as the ventriculus, or cliylific ventricle. 



The remaining part of the alimentary canal is the intestine. This 

 is often composed of three specialized regions, named, as in the 

 higher animals, the ileum or small intestine, the colon or large intes- 

 tine, and the rectum. 



There may be several sets of appendages to the alimentary 

 canal. The first of these are the salivary glands, which open near 

 the mouth. These glands vary greatly in form and number, and 

 are sometimes wanting. In Lepidopterous larvae they constitute 

 the silk glands, and, in this case, have a distinct opening through the 

 modified labium or " spinneret." At the beginning of the stomach, 

 there are in many insects several pouch-like appendages, the ccecal 

 tubes. These secrete a digestive fluid, which resembles the pancre- 

 atic juice of Vertebrates. Usually the most conspicuous of the 

 appendages of the alimentary canal are certain long, slender tubes 

 opening into the beginning of the small intestine, and floating free 

 in the body-cavity or lying upon the surface of the stomach. These 

 are named the MalpigJiian vessels, in honor of Malpighi, an anato- 

 mist who wrote more than two hundred years ago. Formerly they 

 were supposed to be biliary vessels ; but their function has been 

 determined to be urinary. There are other glandular appendages, 

 which, as they open into the alimentary canal near its caudal open- 

 ing, are termed anal glands. These probably do not constitute a 



