TRACHEATA 



345 



The larvae are aquatic, and feed on other insects, etc. ; they 

 have well-developed mouth parts. The tracheal system is 

 closed, and the larvae breathe by means of plate-like gUls, 

 which are borne to the number of six or seven pairs on the 

 anterior abdominal segments. The tracheae ramify in these 

 gills, which are moved about in the water, and possibly serve 

 to some extent as locomotor organs. These gills have been 

 regarded by some authorities as structures from which the 

 wings of Insects in general may have originated. 



The larvae moult very frequently, in one species more than 

 twenty times, and live two or three years. They pass into a 

 pupa stage, and from this a winged insect emerges, this is the 

 svhimago, it takes a short flight, and then casts its skin, and 

 gives exit to the imago. The male fertilises the female on the 

 surface of the water, and shortly afterwards the latter drops 

 her eggs into the stream or pond, and then dies. 



Family 4. Ltbellulidae. — The dragon -flies are large 



Fio. 196. 



A. The anterior portion of the body oiAeschna cyanea freed from the puparium. 



B. The tail being extricated. 



