162 BOYS AND GIRLS IN BIOLOGY. 



gullet, and this gullet leads backward into a stomach 

 (Fig. 136), not such a very large stomach either as one 

 might suppose. This opens, again, into an intestine, 

 which runs straight back, as the lobster's. On each 

 side of the stomach and instestines lies a mass of wavy 

 threads (Fig. 136), which seem all tangled together; 

 but they are all quite separate, and each one is a little 

 duct, or tube, and the whole mass is the caterpillar's 

 liver. All these are called the digestive organs, be- 

 cause they help to digest, or make ready, the food. 

 Next, how does the caterpillar breathe? Where are 

 his organs of respiration ? Tou cannot find any gills, 

 as in the mussel and lobster. The caterpillar could 

 not use gills if he had them, for he does not live in the 

 water. On each side of his body you will find a num- 

 ber of openings which look like so many button-holes 

 (Figs. 136, 137). Each one opens into a ringed tube 

 which runs inward. These tubes are crossed by one 

 long tube which runs lengthwise on each side of the 

 body. Then these tubes divide and subdivide, and 

 spread themselves through the whole body, so that, 

 taking up the smallest piece "of the caterpillar, you 

 will find some of these tiny tubes. The air does not 

 enter the body through the mouth, but through these 

 button-holes, or spiracles, in the sides of the caterpillar, 

 and then into the tubes, and so throughout the whole 



