LIBELLULID^ . 



601 



Fiff. 582. 



retaining its prej'. At rest, the terminal half is so bent uji 

 as to conceal the face, and thus the creature crawls about, to 

 all appearance, the most innocent and harmless of insects. 



Not only does the immature dragon-fl}'^ walk over the bottom 

 of the pool or stream it inhabits but it can also leap for a con- 

 siderable distance, and by a most curious con- 

 trivance. By a syringe-like apparatus lodged 

 in the end of the body, it discharges a stream ''\ 

 of water for a distance of two or three inches 

 behind it, thus propelling the insect forwards. 

 This apparatus combines the functions of loco- 

 motion and respiration. There are, as usual, 

 two breathing pores {stigmata) on each side of 

 the thorax. But the process of breathing seems to be mostly 

 carried on in the tail. The tracheae are here 

 collected in a large mass, sending their 

 branches into folds of membrane lining the 

 end of the alimentary canal, and which act like 

 a piston to force out the water. The entrance 

 to the canal is protected by three to five tri- 

 angular horn}' valves (Fig. 582, 9, 10; Fig. 

 583, side view), which open and shut at will. When open 

 the water flows in, bathing the internal gill-like organs which 

 extract the air from the water. This is then 

 suddenly expelled by a strong muscular effort. 



In the smaller genera, Agrion (Fig. 584, side 

 view of false-gill, showing but one leaf), Lestes 

 and Calopteryx, the respiratory leaves, called the 

 tracheary, or false-gills, are not enclosed within 

 the body, but form three broad leaves, permeated 

 by tracheae, or air-vessels. They are not true 

 gills, however, as the blood is not aerated in 

 them. They onl}^ absorb air to supply the tra- 

 cheae, which aerate the blood only within the 

 general cavity of the body. These false gills also 

 act as rudders to aid the insect in swimming. 



It is easy to watch the dragon-flies through their 

 transformations, as thej^ can easity be kept in ^'s- ''^*- 

 aquaria. Little, almost' nothing, is known regarding their 



Fig. 583. 



