136 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



and a pair of sting feelers which probably act as sense organs. 

 The sting is connected by a duct with a poison reservoir which 

 is supplied with poison from a pair of interior glands. 



Wax Plates. On the under side of each of the last four seg- 

 ments of the worker-bee there is a pair of wax plates. The wax 

 issues as a fluid from small glands in these plates. On its 

 issuance it spreads out over the surface of the plates and 

 hardens. It can then be plucked off in thin sheets by the bee. 



THE INTERNAL STRUCTURE OF A CATERPILLAR 



The body of the bee is too small to be dissected easily. 

 For a study of the internal insect anatomy we may take a 

 caterpillar; any kind will do, although one with a naked in- 

 stead of hairy body will be more convenient to use. Although 

 caterpillars are immature insects they are the young stages 

 of butterflies and moths they will reveal all the important 

 organ systems, except one, in well-developed condition. The 

 one exception is the reproductive system, which may be 

 examined in a full-grown grasshopper. 



Adipose Tissue. On opening the body of the caterpillar 

 the first thing noted is a mass of whitish flocculent material 

 which is fat, or adipose tissue. It is formed out of the surplus 

 food eaten by the voracious caterpillar, and is used during the 

 time which the insect spends in the chrysalis stage when it is 

 inactive and cannot feed. This adipose tissue lies all around 

 and over the various internal organs, and must be picked 

 away to reveal them. 



Alimentary Canal. The most conspicuous organ visible, 

 after the fat is removed, is the long straight alimentary canal 

 running from mouth to anus through the middle of the body. 

 It is composed of successive parts, named, beginning at the 

 mouth, esophagus, ventriculus or stomach, small intestine, 

 large intestine and rectum. Where the ventriculus and 

 small intestine join, a few delicate, whitish, thread-like con- 

 voluted tubules arise known as the Malpighian tubules. These 

 correspond in function to the kidneys of other animals, taking 

 up and excreting waste from the blood. 



