ONI 



ONO 



count, according to the circumstances 

 which take place between the agreement 

 for the loan and the day fixed for paying 

 the last instalment. Thus the omnium 

 of the year 1799, was at first at 4 and 5 

 per cent, premium ; on the 20th of Au- 

 gust it had risen to 19|, and on the 3d 

 September was at 22 ; it soon after fell 

 considerably, and on the 14th of October 

 was at 4$, 2i, 3| ; but on the 18th No- 

 vember it had got up again to 12 per 

 cent, premium. The omnium of the 

 year 1801 rose, on the signing of pre- 

 liminaries of peace, to 18 per cent., 

 and was soon after at 25 per cent, 

 premium : the omnium of the following 

 year was at one time at 12 per cent, 

 discount. 



OMPHALEA, in botany, a genus of 

 the Monoecia Monadelphia class and 

 order. Natural order of Tricoccae. Eu- 

 phorbire, Jussieu. Essential character : 

 male, calyx fbur-leaved ; corolla none ; 

 filaments columnar, with the anthers 

 inserted into it : female, calyx five- 

 leaved ; corolla none ; stigma trifid ; cap- 

 sate fleshy, three-celled ; nut solitary. 

 There are four species, all natives of Ja- 

 maica. 



ONCHIDIUM, in natural history, a 

 genus of the Vermes Mollusca class and 

 order. Body oblong, creeping, flat be- 

 neath, mouth placed before ; two feelers, 

 situate above the mouth ; two arms at the 

 side of the head ; vent behind and placed 

 beneath. There is but a single species, 

 viz. O. typhae, the onch, which is describ- 

 ed in the transactions of the Linnaean so- 

 ciety. It inhabits Bengal, on the leaves 

 of the typha elephantina, about an inch 

 long, and not quite so broad, but linear, 

 und longer when creeping. In appear- 

 ance it very much resembles a limax, but 

 differs principally in wanting the shield 

 and lateral pore, and in being furnished 

 with a vent behind. Body above con- 

 vex; head small and placed beneath, 

 which when the animal is in motion is 

 perpetually changing its form and size, 

 and drawn in when at rest ; mouth placed 

 lengthways and continually varying its 

 shape from circular to linear ; feelers re- 

 tractile, resembling those of the slug, and 

 apparently tipt with eyes; arms dilatable, 

 solid, compressed, and palmate when 

 fully expanded. 



ONION, in botany, see ALLTUM. Con- 

 sidered chemically it may be observed, 

 that as it possesses most of the proper- 

 ties of GAKEIC (which see) though not in 

 so large proportions, a volatile oil, on 



which its activity depends, might be ex- 

 pected, but this has not been found. 

 Water distilled from it yields no oil ; it 

 therefore there is any oil, it must be m 

 very small quantities and soluble in wa- 

 ter. The active principle of the onion acts 

 upon the tin of the alembic in which ex- 

 periments have been made. 



ONISCUS, in natural history, a genus 

 of insects of the order Aptera. Jaw trun- 

 cate denticulate ; lip bifid ; antennae from 

 two to four, setaceous ; body oval, consist- 

 ing of about fourteen transverse seg- 

 ments ; fourteen legs. These insects feed 

 on animal and vegetable matter, and they 

 cast their skin. There are nearly fifty 

 species divided into sections. A. with- 

 out feelers; four antennae, sessile. B. feel- 

 ers unequal, the hind-ones longer ; an- 

 tennae filiform. The most common spe- 

 cies is the O. asellus, or common wood- 

 louse, found in great quantities under the 

 bark of decayed trees, beneath stones in 

 damp situations. It preys on minuter in- 

 sects. O. armadillo, the medical wood- 

 louse, is of a darker colour than the for- 

 mer, but found in similar situations. 

 When suddenly disturbed or touched, it 

 rolls itself up into a round form in the 

 manner of the armadillos ; frequently re- 

 maining in that state for a considerable 

 length of time. This insect was former- 

 ly considered as a specific in many disor- 

 ders, but is now rarely used. Among 

 marine insects of this genus, is the O. 

 guadeloupensis, measuring about one 

 inch and three quarters in length ; an- 

 tennae very short, compressed, inferior 

 pair rather longer; abdomen covered 

 with six scales, beneath ; tail somewhat 

 ovate, flat, furnished with a lateral style 

 on each side, the last joint of which is bi- 

 fid ; the five segments of the body before 

 the tail are much narrowed, and destitute 

 of feet. The female protects her young, 

 for a considerable time after their exclu- 

 sion, under the abdominal scales ; in this 

 respect resembling the opossum amongst 

 the quadrupeds. They are often found 

 in the mouth of the Clupea menhaden or 

 mossbanker, attached to the palate, and 

 partaking of its form. 



ONOCLEA, in botany, a genus of the 

 Cryptogamia Filices class and order. Na- 

 tural order of Filices or Ferns. Generic 

 character : capsules under the recurved 

 and contracted pinnules of the frond, re- 

 sembling pericarps. There are two spe- 

 cies, viz. O. sensibilis, and O. polypodioi- 

 des ; the former is a native of Virginia, 

 the latter was found by Koenig, in 

 the fissures of the rocks near the top of 



