76 ODONATA. 



will be seen farther on. The size and concentration 

 of these two rings of the thorax are correlated with 

 great powers of flight, the dragon-fly being one of the 

 swiftest fliers. Fig. 35, i"", is the mesothoracic spiracle. 

 The abdomen (PL III., Fig. 32, C) is long, and in this 

 species somewhat flattened ; it is used by the insect in 

 steering its course. On either side is a fold like that 

 described in the locust, and the mode of breathing in 

 the two insects is similar (see p. 40). 



The abdomen consists of ten distinct rings, though in 

 a dorsal view there appear to be twelve, owing to the chiti- 

 nous ridges which extend transversely across the second 

 and third rings. These, however, are not continued across 

 the ventral surface, and the boundaries of the true rings 

 are determined by sutures. The latter, though less dis- 

 tinct than the ridges, are seen, on careful examination, 

 extending entirely round the abdomen. Besides the circu- 

 lar ridges there is a longitudinal ridge on each side of the 

 abdomen, and another extending along the middle of the 

 back, as seen in PI. III., Figs. 31, 32. This last-mentioned 

 ridge is sometimes carried farther forward in the female 

 than in the male, though the former may imitate the male in 

 this particular (as seen in Fig. 32) as well as in the color- 

 ing of the abdomen. These ridges are not only hard, but 

 are toothe.d, the sharp points of the teeth extending back- 

 ward, so that if the nail is drawn over them towards the 

 head, a distinct rasping sound is produced. The circular 

 ridges extend to a deep channel in the ventral surface 

 (which is found in both the male and female), where they 

 curve forward, forming a broken, longitudinal, toothed 

 ridge on either side of the channel as if to protect it. 

 These chitinous ridges and teeth add to the strength of 

 the armor, and give greater rigidity to the extremely long 

 and otherwise weak abdomen. By reference to Fig. t,-^^ 



