WHAT AN INSECT IS LIKE: INSIDE 19 



thick and glandular. It is in this relatively short portion of 

 the tube that the food is both digested and absorbed. 



At the hind end of the stomach is a circle of slender 

 urinary or Malpighian tubules, whose function corresponds 

 to the kidneys in us, since they remove nitrogenous wastes 

 from the blood. These tubes discharge into the food tube 

 at the beginning of the intestine. The remainder of the food 

 tube consists of intestine and rectum. 



Malpighian tubules are peculiar to insects. So also are 

 the air tubes, or tracheae, that extend everywhere throughout 

 the body, sending fine branches into every living tissue. 

 The tracheae are lined with thin chitin and are connected 

 with breathing pores on the outside of the body (or else, 

 with tracheal gills), and their function is that of supplying 

 oxygen to the tissues. The insect has no lungs, and no 

 capillary blood vessels: for moving the blood about in the 

 body it has only the single, simple tube called a dorsal vessel. 

 This receives the blood through slit-like valves on its sides, 

 and by pulsating, pushes a current forward out of its open 

 front end toward the brain. There are no capillary blood 

 vessels to carry the oxygen, as in us; but the open tracheae 

 carry it directly to the tissue; hence, the completeness of 

 their distribution, and the fineness of their ultimate branch- 

 ing. In our cross-section diagram on page 25 a few of the 

 larger tracheal trunks are shown. 



The cast skin of a stoneMy, left behind by the adult at 

 transformation (see the lower righthand figure on page 4) 

 will furnish the evidence that the front part of the food tube 



