D R O 
DUG 
. The mofi: curious and extraordinary period of 
the hie of this infeft, is tliat wliich it paffes before 
cornniencing a denizen of the f!<.y. The ufual ex- , 
terior form of the fly-vvorms of this genus v/as lono; 
ago fufficiently known to the generality of natura- 
lifts; but they declined troubling themfelves with 
any minute inveftigation of it, and appear indeed 
to havebeen ignorant that thefe creatures poffeffed 
fcveral peculiarities worthy of altention. The fub- 
ftances among Vv'hich they are found are the m.oil 
oS'enn.ve and naufeous; and the infefts, in this flate, 
belong to the clafs of thofe with variable heads. 
But their grand diftinftion from all others confifts 
in their long and llendcr tails, which at different 
periods appear of diftinft lengths; yet they are in- 
variably longer than their bodies, round, fmooth, 
extremely fmall at their extremities, and fomewhat 
refembling thofe of ratS; whence the whole clafs 
has fometimes received the appellation of rat-tailed 
worms. 
But, in order to underfland the efTential jjroper- 
ties of their tails, it is neceflary firft to acquire a 
knowledge of the worms themfelves. Thefe crea- 
tu-res having been ufiially found on dry ground, 
and only accidentally oblcrved for a great number 
of years, prepoileffed mankind with a notion that 
they were far lefs numerous tlian they really arc; 
nor had any idea occurred that they inhabited the 
vv'atcr. However, on examining vefTels of that 
fluid in a corrupted and ftinking'flate, they have 
been there found in great numbers, lying among 
the mud at their bottoms ; and, on being removed, 
and immerfed in water of a purer nature, they have 
foon evinced the neceffity and utility of their long 
tails. 
Notwidiftanding thefe worms are capable of 
living in mud under water, it is certain that they 
are under a necefTity of inhaling frefli air, like other 
water fly- worms: and to this efTential purpofe their 
,long tails contribute; for while they lie buried in 
the foil, thefe members are extended upwards to 
the furface of the water; and, having apertures at 
their extremities, the air is thereby admitted into 
tliC bodies of the infe6ls. It is, indeed, very amuf- 
ing to obierve thefe animals, after being put into 
water, quickly defcending to the bottom, and as 
ipeedily thrufting up the extremities of their tails 
to the outfide. From the circumPcance of their 
being able to reach tlie furface, though from what- 
ever depth, we may rationally conclude that they 
are endowed with the faculty of extending their 
tails at pleafure to any length : and the way to ai- 
certain tliis conclufion feems very eafy, namely, by 
increafing the depth of the water; for, as the worms 
delight to lodge at the bottom, if they are inclined 
to remain, they are fpeedily compelled to lengthen 
their tails proportionably, in order to breathe from 
the furface. A repetition of this experiment v/iil 
prove that each of thefe worms is capable of flretch- 
ing it's tail to the length of five inches ; an amazing 
extent for a creature v/hofe body is not above half 
an inch; and the tail of which, in it's natural ftatc, 
does not much exceed that length. Flowever, five 
inches is the utmoft exertion of any one of thefe 
infefts in this action; and when the water in the 
vefTel is rendered deeper, they either quit the bot- 
tom, and crawl up the fides to a proper height, or 
elfe continue to fwim at the depth of five inches. 
The organization of lb remarkable a part of this 
animal as it's tail, cannot but appear to t!ie curious 
as an objedt v/orthy their attention; and tlie natu- 
ral tranlparency both of that and of the body of 
this infeft, muft greatly facilitate the examination; 
Indeed, with refpect to many of the younger of* 
thefe worms, and fuch of them as have not ar- 
rived at that ftate in which they quit the water, 
the p:irts are almoft as eafiiy diflinguifhable within 
the body as if placed within a glafs tube. It is no 
difficult matter, in every ilate of this worm, to 
perceive that the tail is compofed of two hollow 
tubes; one of v/hich nicely fits, and is eafiiy re- 
trailed within the other, or protracted, as the occa- 
fions of the animal may require. The exterior, 
and confequently the larger tube, feems to be an 
elongation of the fiefliy matter which forms the 
rings of the body: within this there is a fmaller 
tube, chiefly of a blackifli brown colour; and, by 
means of the variation in hue, they may be diftin- 
guiflied from each other even when fiiut up. The 
interior tube may with propriety be called the tube 
of refpiration, as it is capable of being lengthened 
or fhortened for that purpofe at pleaflire; the ex- 
terior one ferving only for a cafe or flieath. Nor 
is this all : it is eafiiy known that thefe pipes are in 
themfelves capable of extenfion; by obferving, 
that while the v/hole interior tube is lodged within 
the cafe, it is of no determinate length, but fome- 
times long, and at others fhort. 
Numbers of the aquatic fly-worms do not quit 
the water till they arrive at their perfect ftate ; but 
this kind, as foon as they have acquired their 
proper growth, leave that fluid, and crawl abroad 
on the earth. Their bodies, in this new element, 
become dirty and greenifli; and, when they have 
found a pi-oper fpot which is foft and moift, they 
there inhume themfelves; and, after undergoing 
their necefTary transformations, burit out in the 
fliape of flies. Their changes are all accomplifhed 
under iliells of their own Ikins, which in a few 
hours begin to harden, and by degrees become 
very firm; and they are remarkable for each having 
four horns, two longer and two fhorter, placed in 
different direftions near the head, which ferve as 
the organs of refpiration to the inclofed nymph. 
There are feveral fpecies of this genus of flies, 
no lefs different in their fizes than in the worms 
from which they are produced: the largeft of thefe 
are found in vaults and privies ; and in winter vaft 
numbers of them take up their abodes in the hol- 
lows of willows, and other trees which grow conti- 
guous to rivers and marfhes. 
DRONTE. See Dodo. 
DUCK. A very large genus of birds of the 
order of anferes. The characters are thefe: the 
beak is fhorter in proportion than that of the goofe, 
ftrong, flat or depreffed, and commonly furnifhed 
with a nail at the extremity. The feet are propor- 
tionably larger than thofe of the goofe kind, the 
middle toe being the longeft ; the legs are fhorter, 
and placed farther backwards; the back is flatter; 
and the body is more compreffed. The noitrils 
are fmall and oval ; and the tongue is broad, the 
edges near the bafe being fringed. There are nu- 
merous fpecies of this genus; iome inhabiting 'the 
frefh water, and others the iea. 
D u c K , T A M E . T ame D u cks are re ared with more 
facility than perhaps moff other domeftic animals. 
The very infl:in6ts of the young direft them to 
their favourite element ; and tliough tliey are fome- 
times hatched and conducted by hens, they feem 
to contemn the admonitions of their leaders; which 
circumftance evinces that all birds receive their 
manners rather from nature than education,- The 
falcon does not purfue it's prey becauft it is thus 
taught 
