COLEOPTERA. 
407 
entirely covered ; the body is always oval, the eyes but slightly pro- 
minent, and the thorax much wider than long. The terminal hook 
of the maxillae is arcuated from its base ; those at the extremity of the 
tarsi are often unequal. 
They compose the genera Dytiscus and Gyrinus of Geoffrey. They 
pass their first and last stage of existence in the fresh and placid 
waters of lakes, marshes, ponds, &c. They are good swimmers, and 
rises occasionally to the surface of their liquid abodes in order to 
respire ; this they easily effect by keeping their head motionless, and 
permitting themselves to float. Their body being reversed, they 
elevate its posterior extremity a little above the water, raise the ex- 
tremity of their elytra, or depress the end of the abdomen, in order 
that air may enter the stigmata, which are covered by them, whence 
it finds its way to the tracheae. They are excessively voracious, and 
feed on small animals inhabiting the same element, which they never 
leave excepting during the night, or at its approach. When taken 
from the water they diffuse a nauseating odour. They are frequently 
attracted into houses by the light of candles, &c. 
Their larvae have a long and narrow body composed of twelve 
rings, the first of w'hich is the largest ; a stout head, provided with 
two powerful mandibles, curved into an arc, and perforated near the 
point ; small antennae, palpi, and six simple approximated eyes on 
each side. They have six tolerably long legs, frequently fringed 
with hairs, and terminated by two small nails. They are active, 
carnivorous, and respire either by the anus or by a kind of fins re- 
sembling branchiae. When about to enter into their pupa state they 
leave the water. 
This tribe consists of two principal genera : — 
Dytiscus, Geoff. 
The Dytisci have a filiform antennae longer than the head, two 
eyes, the anterior legs shorter than the folloAving ones, and the last 
most commonly terminated by a compressed tarsus ending in a point*. 
By means of their legs fringed with long hairs, the two last particu- 
larly, they are enabled to swim with gn'at velocity. They dart 
upon other Insects, aquatic Worms, &c. In most of the males the 
three first joints of the four anterior tarsi are widened and spongy 
* According to M. Leon Diifour, their crop is terminated behind by an annular 
roll (bourrelet) a character not found in the preceding tribe. Their csecum forms a 
natatory bladder. Their pectus contains two pneumatic sacs, while the tracheae of 
the other parts are tubular. The adipose splanchnic tissue possesses the characters 
of a true epiploon or mesentery. Their stigmata also differ from those of the 
Terrestrial Carnivora. 
