7 6 



ANIMAL BIOLOGY 



The abdomen in various species consists of from five 

 to eleven overlapping rings with their foldlike joints be- 

 tween them. Does each ring overlap the ring in front 

 or the one behind it ? 



The food tube (Fig. 127) begins at the mouth, which 

 usually bears salivary glands (4, Fig. 127, which repre- 

 sents internal organs of the grasshopper). The food tube 

 expands first into a croplike enlargement; next to this 

 is an organ (6, Fig. 127), which resembles the gizzard 



FIG. 127. VISCERA OF 

 GRASSHOPPER. Key 

 in text. Compare with 

 Fig. 114. 



FIG. 128. AIR TUBES OF INSECT. 



in birds, as its inner wall is furnished with chitinous teeth 

 (b t Fig. 1 14). These reduce the food fragments that were 

 imperfectly broken up by the biting jaws before swallow- 

 ing. Glands comparable to the liver of higher animals 

 open into the food tube where the stomach joins the small 

 intestine. At the junction of the small and large intestine 

 (9) are a number of fine tubes (8) which correspond to 

 kidneys and empty their secretion into the large intestine. 

 The breathing organs of the insects are peculiar to 

 them (see Fig. 128). They consist of tubes which are 



