THE LOCUST OR THE CRAYFISH. 65 



The writer suggests that only a general identification of the 



larger organs be made, and that the internal anatomy of the 



crayfish be taken up with some thoroughness instead. The 



crayfish is larger and the organs can be more readily 



identified. 



With some care the following sets of organs may be identified 



in the grasshopper (see also Figs. 5 and 6). 



The digestive system: note its regions, the outgrowths of 



these, and the probable function of each. (The excretory 



system is associated with the digestive.) 



FIG. 6. Diagram of cross-section of locust in posterior part of thorax. a, 

 first joint of leg; bw, body wall, made up of cuticula, skin, and muscle; c, gastric caca; h, 

 heart; /, spaces in body cavity occupied by air sacs, fat bodies, or blood; 5, spiracle 

 opening into the tracheal tubes (1-3) which carry the air to the various parts of the 

 body; s.g., salivary glands; v.g., ventral ganglion; w, wing. 



The respiratory system consisting of the spiracles which 

 are external, the tracheal tubes, and the air sacs. These 

 glistening tubes make a very complex network, going to all 

 portions of the interior. 



The circulatory system. It is not easy for the beginner 

 to get a satisfactory view of this. The heart is dorsal and 

 is so close to the body wall that it is likely to be removed 

 with it in dissection. It is much elongated, extending the 

 length of the abdomen. The other blood vessels are rather 

 indefinite spaces. 



