138 OUR HOUSEHOLD INSECTS 



of the oesophagus to the end of the rectum, measures 

 about twice the length of the animal's body. All the 

 earlier part, as far as the end of the gizzard, runs 

 straight through the body without twisting ; but the 

 parts after this are more or less twisted about, in order 

 to accommodate their length and bring the rectum to 

 the middle of the hinder end of the body ; hence that 

 portion of the canal after the gizzard needs unravelling 

 to display its parts. In the figure it is shown in this 

 extended condition, but in nature the rectum would be 

 situated 1 , near to the bundles of Malpighian tubules, 

 and the intestine would be twisted about in that neigh- 

 bourhood. It is impossible in the figure to show all the 

 windings of the Malpighian tubules ; they are not 

 merely clustered about the mesenteron as shown, but 

 their ends are interlaced amongst the breathing tubes 

 and the fat body, and spread all over the abdomen. In 

 all these parts they are bathed by the blood which fills 

 all the cavities of the body, and eliminate from it the 

 nitrogenous waste products, which thus ultimately find 

 their way into the intestine. That part of the alimentary 

 canal extending from the mouth to the end of the gizzard 

 is called the stomatodoBum, and that from the commence- 

 ment of the ileum to the end of the rectum the procto- 

 doeum. Each of these cavities was formed as a gradual 

 growth inwards of a depression of the outer surface of 

 the body ; hence each is lined with a continuation of the 

 chitinous skin which invests the body, and this is, 

 therefore, renewed each time the skin is cast. The 

 mesenteron, on the other hand, originated in a different 

 way, and hence is not so lined. The " teeth " of the 

 gizzard are simply extra hard portions of this chitinous 

 lining. 



In order to complete the sketch already given of the 



