antennae, and is said to come nearer to Carabidae than the previously known forms did, and we may anticipate that a more extensive knowledge will show that the family may find a natural place in the Adephaga. The description of the abdomen given by Raffray is erroneous; in a specimen of the genus _Arthropterus_ the writer has dissected, he finds that there {215}are five ventral segments visible along the middle, six at the sides, as in the families of Adephaga generally. There is said to be a great difference in the nervous systems of Carabidae and Paussidae, but so little is known on this point that we cannot judge whether it is really of importance. [Illustration: Fig. 99.—A, Larva of _Gyrinus_ (after Schiödte); B, under side of _Gyrinus_ sp. (after Ganglbauer). 1, Prosternum; 2, anterior coxal cavity; 3. mesothoracic episternum; 4, mesoepimeron; 5, mesosternum; 6, metathoracic episternum; 7, middle coxal cavity; 8, metasternum; 9, hind coxa; 10, ventral segments. [N.B.—The first ventral segment really consists, at each side, of two segments united; this may be distinctly seen in many Gyrinidae.]] FAM. 11. GYRINIDAE (_Whirligig beetles_).—_Antennae very short; four eyes; middle and hind legs forming short broad paddles; abdomen with six segments visible along the middle, seven along each side._ These Insects are known to all from their habit of floating lightly on the surface of water, and performing graceful complex curves round one another without colliding; sometimes they may be met with in great congregations. They are admirably constructed for this mode of life, which is comparatively rare in the Insect world; the Hydrometridae amongst the bugs, and a small number of different kinds of Diptera, being the only other Insects that are devoted to a life on the surface of the waters. Of all these, Gyrinidae are in their construction the most adapted for such a career. They are able to dive to escape danger, and they then carry with them a small supply of air, but do not stay long beneath the surface. Their two hind pairs of legs are beautifully constructed as paddles, expanding mechanically when moved in the backward direction, and collapsing into an extremely small space directly the resistance they meet with is in the other direction. The front legs of these Insects are articulated to the thorax in a peculiar direction so that their soles do not look {216}downwards but towards one another; hence the sensitive adhesive surface used during coupling is placed on the side of the foot, forming thus a false sole: a remarkable modification otherwise unknown in Insects. They breathe chiefly by means of the very large metathoracic spiracles.