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 gills, 
which are borne to the number of six or seven pairs on the 
anterior abdominal segments. The tracheae ramify in these 
eills, 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 
subimago, 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. LrpenLuLipAE—The dragon- flies are large 
Fic. 196. 
A, The anterior portion of the body of Aeschna cyanea freed from the puparium. 
B. The tail being extricated. 
