ORDER V. COLEOPTERA. — BEETLES. 281 
they keep dry by raising them above the surface. When they wish to 
change their place suddenly, they give their body a quick and vermicular 
movement, beating the water with the tail. They especially feed upon the 
larvee of dragon-flies, gnats, tipulw, aselli, Gc. When the period of their 
transformation has arrived, they quit the water and bury themselves under 
the earth of the adjacent banks, keeping, however, in very damp situations, 
where they form an oval cavity in which they enclose themselves. Accord- 
ing to Resel, the eggs of the Dytiscus marginalis hatch ten or twelve 
days after being deposited: at the end of four or five more, the larva is 
already four or five lines long, and moults for the first time. The second 
change of skin takes place at the expiration of a similar interval, and the 
animal is now as large again as it was before: when full grown it is two 
inches long. In summer it has been observed to become a pupa at the end 
of fifteen days, and a perfect insect in fifteen or twenty more days. 
D. Marginalis. — This is a common species, an inch and a quarter long, 
being of a dark-olive color, with a buff-colored margin entirely round the 
thorax, and a line of the same color on the outer margin of the elytra, which 
are not dilated at the sides; those of the female are furrowed from the base 
about two thirds of the whole length. Fabricius says that the species when 
laid upon its back gains its ordinary position by taking a leap. Esper kept 
a specimen of this insect for three years and a half in good health in a large 
bottle of water, feeding it every week, and sometimes oftener, with bits of 
raw beef about the size of a walnut, upon which it precipitated itself and 
sucked the blood entirely from it. It was able to fast for a month ata 
time. It killed a specimen of Lydrophilus piceus, although as large again 
as itself, by piercing it between the head and thorax, the only part of the 
body without defence. According to Esper, it is sensible to the changes 
of the atmosphere, which it indicates by the heights at which it keeps in the 
bottle. 
Gyninus. — According to Cuvier, this genus comprises those insects which 
have the antennx in a mass, and shorter than the head; the two fore legs 
are long, advanced liked arms, and the four others very short and depressed, 
broader and oar-like. The eyes are four in number; the body is oval, and 
generally very shining; the antennw, inserted in a cavity before the eyes, 
have the second joint exteriorly elongated, like an ear, and the following 
joints (of which seven are only distinctly visible) very short, and closely 
united into a mass nearly like a spindle, and rather bent; the head is in- 
serted into the thorax as far as the eyes, which are large, and divided by a 
ridge on the sides, so that there appear two above and two below; the 
upper lip is rounded, and very much ciliated in front; the palpi are very 
small, and the inner pair of the maxillary are wanting in many species. 
