Let us listen to De Geer. "It walks as fast, when it likes, as other bugs; but generally its walk is slow, and it moves with measured steps. After having taken one step forward, it stops a while, and then takes another, leaving, at each movement, the opposite leg in repose; it goes on thus continually, step after step in succession, which gives it the appearance of walking as if by jerks, and in measure. It makes almost the same sort of movement with its antennæ, which it moves also at intervals and by jerks. All these movements have a more singular appearance than it is possible for us to describe."[23] [23] "Mémoires pour servir à l'Histoire des Insectes." Tome iii., p. 283. 4to. Stockholm, 1773. By means of this disguise, it can approach little animals, which become its prey, such as flies, spiders, bed bugs. [Illustration: Fig. 72.--Pupa of Reduvius personatus, covered with its cloak of dust (magnified).] [Illustration: Fig. 73.--Pupa of Reduvius personatus, denuded of its cloak of dust (magnified).] To see what a curious appearance the _Reduvius_ presents, one should take off its borrowed costume. Then you will observe an entirely different animal, and one which has nothing repulsive about it. With the exception of the hemelytra and wings, which it has not yet got, all its parts have the form which they are to have later, after the wings are developed. Fig. 72 represents, from Charles de Geer's Memoir, the pupa of the _Reduvius personatus_ covered with dust, and resembling a spider; Fig. 73 the same insect cleaned, freed from the cloak of dust which served to disguise it. The _Hydrometræ_ (from [Greek: hydôr], water, and [Greek: metrein], to measure) have linear bodies. The head, which forms nearly the third of the entire length, is furnished with two long antennæ, and armed with a thin, hair-like beak. The legs are long, and of equal length. The reader may have often seen the _Hydrometra stagnorum_ walking by jerks on the surface of the water (Fig. 74). The body and legs are of a ferruginous colour, the hemelytra a dull brown, and the wings hyaline, or glassy, and slightly blackish. Geoffroy says that it resembles a long needle, and calls it the Needle Bug. [Illustration: Fig. 74.--Hydrometra stagnorum.] The _Hydrocorisæ_, or Water Bugs, have the antennæ shorter than the head, or scarcely attaining to its length, and inserted and hidden under the eyes, which are in general of remarkable size. All these Hemiptera are aquatic and carnivorous. We will mention the two principal types, the _Nepæ_, or Water Scorpions, and the _Notonectæ_, or Boatmen.