202 THE DRAGON FLY. 



inflating the thorax at the same time, it bursts the case 

 along the back, and gradually effects its escape ; but it 

 does not entirely leave the case, until its wings, which 

 are at first folded together, have acquired their full ex- 

 tent and lustre, which they speedily do upon exposure 

 to the atmosphere ; and the new-born fly wings away 

 to sport its beauties and continue its ravages. 



The eyes of the dragon fly are singular pieces of 

 mechanism, and admirably adapted for enabling them 

 to see, in all directions, those insects on which they feed. 

 The surface of the eye is reticulated, or divided into a 

 net-work, of which the compartments are regular six- 

 sided figures. It is computed that there are between 

 twelve and thirteen thousand of these in each eye of the 

 species that has been examined ; and that each of these 

 is a distinct and perfect organ of vision, though the 

 whole five and twenty thousand, which the two eyes 

 contain, are for the information of one living principle, 

 and the preservation of one little insect ! 



We are apt to envy the dragon fly his five and 

 twenty thousand eyes, when we think we have but 

 two ; and yet, when we come to reflect upon it, we 

 have the advantage even in the number of our points 

 of vision. The single lens of our eyes is capable of 

 motion in every direction, and with almost instant 

 celerity, over the whole field of vision. The number 

 of points that we can therefore examine without turn- 

 ing the head, is not only greater than that which the 

 eyes of the dragon fly can command, but greater than 

 arithmetic can sum up. 



Such are a few of the most obvious and accessible 

 subjects which offer themselves to human contem- 



