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OES 
O E S 
was drawing it, the smell or effluvia render- 
ed him so giddy, that he was several times 
obl'ged to quit the room, and walkout in the 
fresii air to recover himself; but recollecting 
at la t what might be the probable cause of 
his repeated illness, he opened the door and 
window's of the room, and the free air then 
enabled him to liaish his work without any 
more returns of the giddiness. Mr. Lighl'- 
foot informs us, that he has given a spoonful 
of the juice of this plant to a dog, but with- 
out any other effect than that of making him 
■very sick and stupid. In about an hour he 
recovered ; and our author has seen a goat 
eat it with impunity. To such of the human 
species as have unfortunately eaten any part of 
th s plant, a vomit is the best remedy. 
Lo’bel, Ray, and others, call this vegetable 
cenanthe aquatica cicuhc facie. It grows in 
great plenty all over Pembrokeshire, and is 
called by the inhabitants five-lingered root ; 
it is much used by them in cataplasms for 
the felon or worst kind of whitlow. They 
eat some parts of it, but carefully avoid tire 
roots or stalk. These indeed are of a most 
pernicious nature, and never fail to prove 
instantly fatal unless a proper remedy is ap- 
plied. 
OENOTHERA, tree-primrose: a 
genus of the monogynia order, in the octan- 
ciria class of plants ; and in the natural me- 
thod ranking under the 17th order, calycan- 
themau The calyx is quadrifid ; the petals 
four; the capsule cylindric beneath; the 
seeds naked. There are 11 species; the 
most remarkable of which aye: 1. The bi- 
ennis, or common biennial tree-primrose, 
with large bright-yellow flowers. 2. Octo- 
valvis, or octovalved, smooth, biennial tree- 
primrose, with large bright-yellow flowers. 
3. The fruticosa, or shrubby narrow-leaved 
perennial tree-primrose, with clusters of yel- 
low flowers, succeeded by pedicellated, 
acute-angled capsules. 4. The pumila, or 
low perennial tree-pr'mirose, with bright-yel- 
low flowers, succeeded by acute-angled cap- 
sules. 
These plants are exotics from America ; 
but are ail very hardy, prosper in any com- 
mon soil and situation, and have been long in 
the English gardens, especially the three first 
sorts ; but the oenothera biennis is the most 
commonly known. 
OESOPHAGUS. See Anatomy. 
OESTRUS, a genus of insects of the order 
diptera: the generic character is, antennae 
triarticulate, very short, sunk ; face broad, 
depressed, vesicular ; mouth, a simple ori- 
fice; feelers two, Inarticulate, sunk; tail in- 
flected. The genus oestrus or gad-fly is re- 
markable, like that of ichneumon, for the 
singular residence of its larva? ; viz. beneath 
the skin, or in different parts of the bodies of 
quadrupeds. 
The principal European species is the oes- 
trus bovis, or ox-gadfly. This is about the size 
of a common bee, and is of a pale yellowish- 
brown colour, with the thorax marked by 
four longitudinal dusky streaks, and the ab- 
domen by a black bar across the middle, 
the tip being covered with tawny or orange- 
coloured hairs; the wings are pale brown, 
and unspotted. 
The female of this species, when ready to 
deposit her eggs, fastens on the back, of a 
heifer or cow, and piercing the skin with the 
tube situated at the tip of the abdomen, de- 
posits an egg in the puncture ; she then pro- 
ceeds to another spot at some distance from 
the former, repeating the same operation at 
intervals on many parts of the animal’s back. 
This operation is' not 'performed without se- 
vere pain to (he animal on which it is prac- 
tised ; and it is for this reason that cattle are 
observed to be seized vvi h such violent hor- 
ror when apprehensive of the approaches of 
the female oestrus ; flying with uncontrol- 
able rapidity, and endeavouring to escape 
their tormentor by taking refuge in the near- 
est pond; it being observed that this insect 
rarely attacks cattle when standing in water. 
In the punctures of the skin thus formed 
by the gadfly, the several eggs hatch ; and 
the larva’, by their motion and suction, cause 
so many small swellings or abscesses beneath 
the skin, which growing gradually larger, 
become externally visible, exhibiting so many 
tubercles an inch or more in diameter, with 
an opening at the top of each, through which 
may be observed the larva, imbedded in a 
purulent fluid; its appearance is that of an 
oval maggot, of a yellowish-white colour 
while voung; but growing gradually darker 
as it advances in age, till at the time of its 
full growth it is entirely brown. It is chiefly 
in the months of August and September that 
the eggs are laid, and the larva: remain 
through the ensuing winter, and till the latter 
part of the next June, before they are ready 
to - undergo their change into chrysalis. At 
this period they force themselves out from 
their respective cells, and falling to the 
ground, each creeps beneath the first con- 
venient shelter, and lying in an inert state 
becomes contracted into an oval form, but 
without casting the larva skin, which dries 
and hardens round it. When the included 
insect is ready for exclusion, it forces open 
the top of the pupa or chrysalis coat, and 
emerges in its perfect form, having remained 
within the chrysalis somewh.t more than a 
month. 
Though the history of this insect in its 
larva state has long ago been detailed with 
sufficient accuracy by Vallisneri, Reaumur, 
and others, yet the fly itself appears to have 
been very generally confounded, and that 
even by Linnaeus himself, with a very differ- 
ent species, resembling it in size, but which 
is bred in the stomach and intestines of 
horses, the larvae being no other than the 
whitish rough mgagots which farriers call by 
the title of hots. This insect is the oestrus 
equi ; it is a trifle smaller than the oestrus 
bovis, and is of a yellowish-brown colour, 
with a dusky band across the thorax, and the 
tip of the abdomen of similar colour ; the 
wings are whitish, with a pale dusky bar 
across the middle of each, and two dusky 
spots at the tip. 
The manner in which the young larvae or 
bots are introduced into the stomach and 
bowels of the animal they infest is singularly 
curious. When the female has been im- 
pregnated, and the eggs are sufficiently ma- 
tured, she seeks among the horses a subject 
for her purpose, and approaching it on the 
wing, she holds her body nearly upright in 
the air, and her tail, which is lengthened for 
the purpose, curved inwards and upwards ; 
in this way she approaches the part where 
she designs to deposit her egg ; and suspend- 
ing herself for a few seconds before it, sud- 
denly darts upon it, and leaves her egg ad- 
hering to the hair; she hardly appears to 
settle, but merely touches the hair with the 
egg held out on the projected point of the 
abdomen. The egg is made to adhere by 
means of a glutinous liquor secreted with it. 
She then leaves the horse at a small distance, 
and prepares. a second egg, and, poising her- 
self before the part, deposits it in the same 
way. The liquor dries, and the egg becomes 
urmly glued to the hair; this is repeated by 
various Hies till four or five hundred eggs are 
sometimes placed on one horse. 1 lie horses, 
when they become used to this fly, and find 
ihat it does them no injury (as the’tabani and 
conopes, by sucking their blood), hardly re- 
gard it, and do not appear at all aware of its 
insidious object. r ! he skin of tiie horse is 
always thrown into a tremulous motion ou 
the touch of this insect ; which merely arises 
from the very great irritability of the skin and 
cutaneous muscles at this season of the year, 
occasioned by the continual teasing of the 
flies, till at lens-th these muscles act involun- 
tarily on the slightest touch of any body 
whatever. '1 lie inside of the knee is the part 
on which these flies are most fond of deposit- 
ing their eggs, and next to this on the side 
and back part of the shoulder, and less fre- 
quently on the extreme ends of the mane. 
But it is a fact worthy of attention, that the 
fly does not place them promiscuously about 
the body, but constantly on those parts which, 
are most liable to be licked with the tongue : 
and the ova therefore are always scrupulously 
placed within its reach ; for, when they have 
remained on the hairs four or five days, they 
become ripe, after which time Oie slightest 
application of warmth and moisture is suffici- 
ent to bring forth in an instant the latent 
larva. At this time, if the tongue of the 
horse touches the egg, itsoperculum is thrown 
open, and a small active worm is produced, 
which readily adheres to the moist surface of 
the tongue, and is thence conveyed with the 
food to the stomach. 
These larvae attach themselves to every 
part of the stomach, but are generally most 
numerous about the pylorus, and are some- 
times, though much less frequently, found in 
the intestines. Their numbers in the sto- 
mach are very various, often not more than 
half a dozen, at other times more than a 
hundred, and if some accounts might be re- 
lied on, even a much greater number than 
this. They hang most commonly in clus- 
ters, being fixed by the small end to the 
inner membrane of the stomach, which they 
adhere to by means of two small hooks or 
tentacula. When they are removed from 
the stomach they will attach themselves to 
any loose membrane, and even to the skin 
of the hand. 
The body of the larva is composed of 
eleven segments, -all of which, except the 
two last, are surrounded with a double row 
of horny bristles directed towards the trun- 
cated end, and are of a reddish colour, ex- 
cept the points, which are black. These 
larvae evidently receive their food .at the small 
end, by a longitudinal aperture, which is situ- 
ated between two hooks or tentacula. Their 
food is probably the chyle, which, being 
nearly pure aliment, may go wholly to the 
composition of their bodies without any ex- 
crementilious residue ; though on dissection 
the intestine is found to contain a yellow or 
greenish matter, which is derived from the 
