The _Libellula_, which the illustrious Geoffroy designates "Louisa," is, according to modern entomologists, neither a _Libellula_ nor a _Aeshna_, but a species of _Agarion_,--the _Agarion virgo_ (_Libellula virgo_, Linn.) The Agarions are distinguishable from the Libellula and the Aeshna by their remarkably thin, filiform, and exceedingly elongated abdomen, and by the three ocelli arranged triangle-wise on the top of the head. The "Louisa" (_Agarion virgo_) is by no means uncommon in England, and may be found along the upper course of the Thames, the Avon, and other rivers. It is easily recognised by its frail slender body, shining with metallic blue reflexes. There are numerous varieties, distinguished by their varieties of "light and shade." The spotless green-winged species is the "Ulrica" of Geoffroy. The two sexes are not alike. In the centre of their delicately-reticulated wings the males have a large bluish-brown spot, which is wanting in the females. [Illustration: FIG. 38.--Male and Female of the _Agarion virgo_.] The genera _Libellula_, _Aeshna_, and _Agarion_ compose the small family of the _Libellulites_--a family plainly and conspicuously characterised by the size of their head, and by the two pairs of diaphanous wings of almost equal dimensions (the posterior pair is a _little_ shorter than the anterior), which, while the animal is at rest, are kept horizontally extended. [Illustration: FIG. 39.--"A sunny pool, half-fringed with trees."] These are the characteristics which present themselves to the observant eye at the first glance. Do you doubt me? Betake yourself, when "The bird is building in the tree, And the flower has opened to the bee,"-- betake yourself, I say, to any sunny pool, half-fringed with trees, or pleasant river-margin; go, armed with net and microscope, and, having secured a specimen of these terrors of the insect world, where "The strong on weak, cunning on simple, prey," devote yourself to its patient examination. It is only such an examination that can reveal to us some equally important, but less obvious features of the insect. But to catch a Dragon-fly is not always an easy task; the Libellulæ are very timorous, or else they are suspicious of the prowling naturalist who seeks what he can entrap. Their flight is livelier and swifter than even that of the butterfly: when disturbed in their repose, they fly away abruptly, their wings rustling or crackling like a sheet of parchment; if obstinately pursued, they grow irritated, and in their quick jerking movements exhibit all the rage of the Carnivora.