WHAT AN INSECT IS LIKE: INSIDE 



25 



the alimentary canal upon the floor of the body cavity. 

 Let us now examine these structures. 



I. Study with a microscope the respiratory system of a 

 small living damselfly or 

 mayfly nymph, mounted 

 on a glass slide under a 

 coverglass that is properly 

 supported to prevent 

 crushing. Use the smallest 

 and most transparent 

 specimens for this. The 

 air-filled tracheae stand 

 out sharply as black lines, 

 and are clearly visible even 

 to their finest ultimate 

 divisions (tracheoles).* 

 Observe : 



1. The number and ar- 

 rangement of the 

 principal longitudinal tracheal trunks. 



2. Their principal connections with each other. 



3. Their principal connections with the (dark colored, 

 centrally located) alimentary canal. 



4. Their connections with the legs and with the antennae. 



5. Their connections with the gills. 



6. Focus just beneath the^surface of the head and note 



* Preserved specimens will not do for this because the preservatives 

 replace the air and fill the tracheae, rendering them invisible. 



Fig. 9. — A diagram of a cross section through 

 the abdomen of a damselfly nymph. The chitin of 

 the body wall and of the linings of principal tracheal 

 trunks (t.t.t.t.) is shown in solid black. S, stomach; 

 d.v., dorsal vessel or heart; n, nerve ganglion with 

 outgoing nerves; m.m., muscles;/./., fat; «, urinary 

 (or renal, or Malpighian) tubules; w.w., sections of 

 hind wings. 



