"A dorsal region, raised like a donkey's back, or like the rounded keel of a boat, and covered with a velvety substance, which renders it impermeable, numerous fine fringes which garnish either the hind legs, or the borders of the abdomen and thorax, or lastly in a double row form a crest or comb running down the surface of the belly, and which spread themselves out or fold themselves in at the will of the insect, just like fins, favour both this supine attitude and the accuracy of the swimming movements of the _Notonectæ_. Since Nature--which seems often to delight in producing extraordinary exceptions to her ordinary rules, thus bearing witness to the immensity of her resources--had condemned this animal to pass its life in an inverted position, it was necessary, for the maintenance of its existence, that it should provide it with an organisation in harmony with this attitude. It is also for this object that its head is bent over its chest; that its eyes, of an oval shape, can see below from above; that the front as well as the middle legs, agile and curved, solely destined for prehension, can to a certain extent become unbent by means of the elongated haunches which fix them to the body, and clutch firm hold of their prey with the strong claws which terminate the tarsi." HOMOPTERA. We come now to the second group of the order Hemiptera, namely, Homoptera. The insects which compose this division are numerous. They may be arranged into three great families, of the most remarkable members of which we shall give some account. These are the _Cicadæ_, the _Aphidæ_ or Plant Lice, and the _Coccidæ_. The Cicada is the type of the first of these families. It has a deafening and monotonous song; as Bilboquet says, in the "Saltimbanques," "those who like that note have enough of it for their money." Virgil pronounced a just criticism on the song of the Cicada: he saw in it nothing better than a hoarse and disagreeable sound:-- "At mecum raucis, tua dum vestigia lustro, Sole sub ardenti resonant arbusta cicadis," says the Latin poet in his "Eclogues," and repeats the same opinion in a verse in his "Georgics:"-- "Et cantu querulæ rumpent arbusta cicadæ." The song of the Cicada, so sharp, so discordant, was, however, the delight of the Greeks. Listen to Plato in the first lines of "Phædo:" "By Hera," cries the philosopher-poet, "what a charming place for repose!... It might well be consecrated to some nymphs and to the river Achelöu, to judge by these figures and statues. Taste a little the good air one breathes. How charming, how sweet! One hears as a summer noise an harmonious murmur accompanying the chorus of the Cicada."