DES 
DES 
gined; head iuflected, and hidden under 
the thorax. Gmelin has enumerated about 
90 species, in three sections. A. jaw bi- 
fid. B. jaw one-toothed. C. feelers four, 
clavate, the last joint larger. This genus 
consists principally of small insects. Their 
larvae are found among skins, furs, and va- 
rious animal substances of a dry kind, 
which they injure, and on which they live. 
They are exceedingly destructive to books, 
furniture, and collections of natural his- 
tory. In the grab state they are of a length- 
ened oval shape, and hairy, especially to- 
wards the end of the body. Tlie complete 
insect has the habit of withdrawing the head 
beneath tlie thorax when handled. D. lar- 
darius is something less than half an inch in 
length, and of a dusky brown colour, with 
the upper half of the wing-shells whitish, 
marked vrith black specks. The larva is 
found on dried and salted meat : and is a 
sad pest to museums, libraries, and prepa- 
rations of natural history. D. pellio may 
be seen almost every where in the spring ; 
it is less than the lardarius, and is black, 
with shells having each a white spot : the 
larva oblong, hairy, with a bristled tail. 
DERRIS, in natural history, a genus of 
the Vermes Mollusca. Generic character : 
body cylindrical, composed of articulations ; 
mouth "terminal ; feelers two. There is only 
one species. D. sanguinea, found on the 
coast of Pembrolj.eshire. Body cylindri- 
cal, gradually tapering to a point behind, 
composed of joints, and capable of great 
inflexibility, covered with a membranaceous 
transparent coat, through which the inter- 
nal parts are visible ; head extended beyond 
the outer skin, less than the anterior part 
of the body, to which it is connected by a 
membranaceous covering, forming a neck. 
It moves by an undiilatory motion of the 
whole body. 
HERVIS, a name given to all Moham- 
medan monks, though cf various orders. 
DESCENSION, in astronomy, is either 
right or oblique. Right descension is an 
arch of the equinoctial, intercepted be- 
tween the next equinoctial point and the 
intersection of the meridian, passing tlirough 
the centre of the object, at its setting, in 
a right sphere. Oblique descension, an 
arch of the equinoctial, intercepted between 
the next equinoctial point and the horizon, 
passing through the centre of the object, at 
its setting, in an oblique sphere. 
DESCEN SIGNAL differeme, that be- 
tween the right and oblique descension of 
any heavenly body. See Descension. 
DESCENT, in general, is the tendency 
of a body from a higher to a lower place ; 
thus all bodies, unless otherwise determined 
by a force superior to their gravity, descend 
towards the centre of the earth : the planets 
too may be said to descend from their aphe- 
lion to the perihelion of their orbits, as the 
moon does from the apogee to the perigee. 
Heavy bodies, meeting with no resistance, 
descend with an uniformly accelerated mo- 
tion, for the laws of whicb- see Mecha- 
nics. 
Descent, or hereditary succession, is 
the title of which a man on the death of his 
ancestor acquires his estate by right of re- 
presentation, as his heir at law : and an 
estate so descending to the heir is in law 
called the inheritance. 
Descent is of three kinds ; by common 
law, by custom, or by statute. By com- 
mon law, as where one hath land of inheri- 
tance in fee-simple, and dieth without dis- 
posing thereof in his life-time, and the land 
goes to the eldest son and heir of course, 
being cast upon him by the law. 
Descent of fee-simple by custom, is some- 
times to all the sons, or to all the brothers 
(where one brother dieth without issue), as 
iu gavel-kind ; sometimes to the youngest 
son, as in borough English ; and sometimes 
to the eldest daughter, or the youngest, ac- 
cording to the customs of particular places. 
Descent by statute is of fee-tail, as di- 
rected by the statute of Westminster, 
2. de donis. 
Descent, in genealogy, the order or suc- 
cession of descendants in a line or family ; 
or their distance from a common progeni- 
tor. Thus we say, one descent, two de- 
scents, &:c. 
Descent, in heraldry, is used to express 
the coming down of any thing from above ; 
as, a lion en descent, is a lion with his head 
towards the base points, and his heels to- 
wards one of the comers of the chief, as 
if he were leaping down from some high 
place. 
Descent, in fortification, are the holes, 
vaults, and hollow places made by under- 
mining the ground. 
The descent into the moat or ditch is a 
deep passage made through the esplanade 
and covert-way, in form of a trench, where- 
of the upper part is covered with madriers 
and clays, to secure the besiegers from the 
enemy’s fire. In wet ditches this trench is 
on a level with the surface of tiie water, but 
in dry ones it is sunk as deep as the bottom 
of the ditch. 
