80 Dragon-flies and Damsel-flies 



as well as forward, and by a special sort of articulation of the head on the 

 thorax it can be rotated readily through 180, so that the principal part of 

 each eye can be directed sidewise or even straight down. For accurate 

 flight and successful pursuit of flying prey the dragon-fly has full need of 

 good eyes. It is to be noted, too, that the eyes are relatively largest in those 

 particular dragon-fly kinds which have the most powerful flight. On the 

 head, also, are three simple eyes (ocelli), the pair of very small awl-like 

 antennae, and the great mouth. The mouth is overhung as by a curtain 

 by the large flap-like upper lip (labrum). The jaws (mandibles) are strong 

 and toothed, and obviously well adapted for tearing and crushing the cap- 

 tured prey. 



When the prey is come up with, however, it is caught not by the mouth 

 but by the "leg-basket." The thorax is so modified, and the insertion of 

 the legs such, that all the legs are brought close together and far forward, 

 so that they can be clasped together like six slender, spiny grasping arms 

 just below the head. Although the catching and eating is all done in the 

 air and very quickly, observers have been able to see that the prey is caught 

 in this "leg-basket" and then held in the fore legs while being bitten and 

 devoured. These slender legs are used only very slightly for locomotion, 

 but they serve well for the light unstable perching which is characteristic 

 of the dragon-flies. 



The internal anatomy is specially characterized, as might well be 

 imagined, by a finely developed system of thoracic muscles for the rapid 

 and powerful motion of the wings and the delicate and accurate move- 

 ments of the legs. The respiratory system is also unusually well developed, 

 such active insects needing a large quantity of oxygen, and generating a 

 large amount of carbon dioxide. The respiratory movements, according 

 to Calvert, consist in an alternate expansion (inspiration through the ten 

 pairs of breathing-holes, or spiracles, arranged segmentally on thorax and 

 abdomen) and contraction (expiration) of the abdomen. The rate of 

 movement varies greatly at different times owing to unknown causes, but 

 is always quickened by exercise, increased temperature, or mechanical irri- 

 tation. In different dragon-flies the inspirations have been noted to be 

 from 73 to 118 a minute. 



The dragon-flies are famous for their beautiful metallic colors. As they 

 dart through the air one gets glimpses of iridescent blue and green and cop- 

 per, of tawny red and violet and purple reflections that are most fascinating 

 and tantalizing. Seen close at hand in the collections, however, they are 

 mostly dull-colored and, except for their "pictured" wings and the sym- 

 metry and trim outline of their body, rather unattractive "specimens." But 

 a freshly caught dragon-fly shows the real glory of the coloring: delicate 

 changing shades of green and violet and copper quiver in the great eyes; 



