The _Nepa cinerea_ (Fig. 75), which Geoffroy calls the Oval-bodied Water Scorpion, and which he also designates by the name of the Water Spider, is very common in the stagnant waters of ponds and ditches. Its body, oval, very flat, of an ashy colour, with red on the abdomen, is four-fifths of an inch long. The hemelytra are horizontal, coriaceous, and of a dirty grey colour. Its front legs, with short haunches, and very broad thighs, are terminated by strong pincers, which give to the insect a strong resemblance to the scorpion. It is by folding back the leg and the tarsus under the thigh, that the animal holds its prey, and sucks it with its rostrum or beak. [Illustration: Fig. 75.--Nepa cinerea.] This rostrum is composed of three joints, and contains four pointed bristles. Two present on one side a sort of narrow sharp blade, and have teeth towards their base. Of the two others, the one is a thin smooth needle, the other is provided with hairs directed backwards and forwards. It is with this rostrum, which resembles a case of surgical instruments, that the _Nepa_ pierces and sucks little aquatic insects, not even sparing its own species. Its wound is painful to man, but not in the least dangerous. With its four hind legs the _Nepa_ swims, but at a very slow pace. It generally drags itself along the bottom of the water, on the mud, and does not avoid the hand put out to seize it. Its body is terminated by a tail, composed of two grooved threads, which, when applied together, form a tube, capable of being moved from side to side. Through this canal it breathes the outer air; it puts the end of it out of the water, and the air enters it by inspiration. Some very small hairs, with which the interiors of the grooves are lined, interlace each other, and prevent the water from penetrating into the canal. It is probable that this same canal serves also for depositing the eggs. These last resemble small seeds, covered with points, and are buried in the stalks of aquatic plants. Next to the _Nepa_ comes the _Ranatra_, with a cylindrical, elongated, linear body, with very long and very thin hind legs, and of which one species, which Geoffroy calls the "aquatic scorpion with an elongated body," is common everywhere in stagnant waters in spring. It is brownish, carnivorous, and very voracious. [Illustration: Fig. 76.--Corixa striata.] We must now mention the genus _Corixa_, of which one species, the _Corixa striata_, is very common. This insect walks badly and slowly on land, but swims and cuts through the water with a prodigious rapidity. However, it is not to delay over this last species that we have here mentioned the name of this genus. Some insects which belong to it, and which are found in Mexico, deserve to be alluded to, on account of certain peculiarities which their eggs present. A naturalist, M. Virlet d'Aoust, has published the following details on this subject:--