338 NATURAL ARRANGEMENT OF INSECTS. 



general characters to combine the successive groups, we 

 shall treat the sub-families independently of each other. 

 (300.) The insects constituting the LibellulincB are 

 well known to all persons who knowany thing of the coun- 

 try, as dragon flies. They are essentially flying insects; 

 and the four powerful organs whereby they accomplish 

 this faculty, consist of usually a pellucid glassy mem- 

 brane, which is closely and thickly covered with a reti- 

 culation of nervures ; whence, KGLT et&xfir, as the most 

 typical members, they give a name to the entire group 

 called from them Neuroptera. In velocity of flight, 

 and the power of its protracted continuance, they doubt- 

 lessly exceed all other insects; and Leeuwenhoek re- 

 cords an instance of a swallow being unable to overtake 

 one, which it continued in pursuit of for some time. 

 They have been divided into two groups, of which Li- 

 bellula and Agrion form the respective types, a sub- 

 division supported, in some degree, by differences in the 

 structure of their larvae. The characters, upon which 

 it is founded in the perfect insect, are, that in the former 

 the head is globose, and, in repose, the wings have a hori- 

 zontal distended position ; whereas, in Agrion, they are 

 united vertically over the body, like the butterflies, and 

 their head is transverse. Several exotic species of the 

 latter genus are remarkable for the length and slender- 

 ness of their bodies: thus, the Agrion Lucretia from the 

 Brazils is 5 inches long, and its body scarcely more 

 than the eighth of an inch thick. These gay insects 

 may be observed sporting in every variety of evolution 

 over ponds and brooks, to which they give considerable 

 animation; and it is here that their entirely aquatic larvae 

 pass their lives. These, which undergo an incomplete 

 metamorphosis, progressively acquire the rudiments of 

 wings; and when they have attained their full growth, 

 they creep up the stem of some water plant, and fixing 

 firmly by their legs, the skin splits down the back, and 

 the perfect insect creeps out. A very short time suf- 

 fices to expand its wings, and it then sweeps forth a 

 denizen of the air. In this state it is remarkable for its 



