HELMINT 
furface of the fluid, and others fwim in it, is aftoniftiing; 
nor is the celerity of the various fpecies of animalcula 
infuforia lefs deferving of admiration. 
It appears that Linnaeus was at confiderable pains in 
colle£ting every difcovery made by his cotemporaries in 
this region of invifible animals, in order to form them 
into that excellent arrangement under which we now 
find them in his Syftema Naturae; where they Hand un¬ 
der the following genera: viz. 
Brachionus. A minute worm, endued with the 
power of dilating and contracting its body, which is de¬ 
fended by a fhell, and furniflied with rotatory cilia. 
There are twelve fpecies, one of which, Brachionus urceo- 
laris , is exhibited in the Helminthology Plate VI. fig. r. 
This is found in clear Itagnant water, juft vifible to the 
naked eye, appearing like a lucid fpeck. Under the 
magnifier it appears of a greenifh yellow, bell-fhaped, 
tail long and bifid at the tip ; fhell toothed at the top, 
and rounded at the bafe; head furnilhed with double 
rotatory organs, which it can protrude or conceal at 
pleafure. The economy of this little animal may ferve 
to elucidate that of the whole infuforia tribes. We may 
confider it as divided into a head, thorax, and abdo¬ 
men; each of which may be extended and contracted 
confiderably : it can, by dilating all three, protrude the 
head beyond the (hell; or, by contracting them, draw 
the whole body within it. The head, when extended 
completely, divides the two rotatory branches ; between 
which comes out a kind of probofcis, armed with two 
fets of fibrils, that appear, when at reft, like a broad 
point; but which can be moved to and from each other 
very brifldy with a vibratory motion, at the will of the 
animal. The form and fituation of the two branches 
are fometimes changed, the end thereof becoming more 
round, and the vibratory motion is then altered to a ro¬ 
tatory one. The thorax is annexed to the lower part 
of the head ; it is mufcular: within it there is a moving 
inteftine, which has been fuppofed to be analogous to 
the lungs or heart. A communication is formed be¬ 
tween the thorax and the abdomen by means of a (liort 
veffef, whofe alternate contractions and dilatations occa- 
fion the abdomen to rife and fall, having at the fame 
time a fort of periftaltic motion. The food is conveyed 
through this veflel into the abdomen, where it is di- 
gefted; it is then difcharged by the anus, which is 
placed near the tail. For greater ftrength its tail is fur¬ 
niflied with three articulations, and is cleft or divided 
at the extremity, by which means it can better fatten 
itfelf to fuitable objeCts. It is in general projected from 
the lower end of the fhell, moving nimbly to and fro, 
and ferving the animal as a rudder when it is fwimming ; 
but, when attached by its glutinous matter to any firm 
fubftance, it enables the animal to enjoy the full exer- 
cife of its curious rotatory motion or play. When the 
little creature has a mind to compofe itfelf to reft, it 
contracts the head and fore-part of the body, brings 
them down into the (hell, and pulls the tail upwards, 
fo that the whole of the animal is contained within the 
ftiell. This valve is fo tranfparent that the termination 
of the edges cannot be eafily diftinguiflied ; but what¬ 
ever is tranfaCted within the ftiell, is as plain as if there 
were no fubftance between the eye and the interior parts; 
infomuch that even the fibrillae may be feen within the 
margin of the fhell. Under a ftrong magnifier its ova¬ 
ries are plainly diftinguifhed at the lower part of the 
body, like three opaque oval fpots, generally fituated 
near the tail. From thefe the young ones burft into 
life ; and it is wonderful to fee them: the inftant, or in¬ 
deed even before, they are loofened from their integu¬ 
ment or bag, they fet their little rotatory wheels in mo¬ 
tion, and appear to have at once all the activity and 
inftinCts of the parent worm! 
Thefe are thy glorious works, parent of good, 
Almighty! Milton, 
Vol.IX. No. 591, 
HOLOG Y. 361 
Vorticella. A naked worm, -with rotatory cilia, 
capable of contracting at^jl extending itfelf. This genus 
contains fifty-feven fpecies, clafled in three divifions: 
ift. Thofe with the body feated on a pedicle or ftem, 
but varioufiy difpofed ; as (hown in the Engraving at 
fig. 2, viz. Vorticella cyathiva , cup-fhaped, tranfparent 
blue, witli a twifted ftem, in three pofitions. Fig. 3, 
Vorticella putrida, oblong, pale blue, with a retraCtil.e tip- 
and rigid ftem, in three pofitionS. Fig. 4, Vorticella pa-' 
tellina, faucer-fhaped, pale blue, with a retortile ftem, in 
three pofitions: thefe three fpecies are commonly found 
in fea-water after it has been kept (landing for a few 
days. 2dly. Thofe furniflied with a tail, as reprefented at 
fig. 5, Votticella jlofculofa , oblong, pale yellow, with a few- 
opaque dots; tail pointed, and rough: found in wet fenny 
lands; juft difcernible to the naked eye. 3d!y. Thofe 
without tail or ftem, as delineated at fig. 6, Vorticella 
ampulla , formed like an afcidia, pale yellow, contained 
in a bottle-ftiaped pellucid greenifh bag; head divided 
into two lobes, ciliated or fringed. The bag is in the 
fhape of a common water-bottle, enveloped in a kind of 
thin film or membrane ; found in foul ftagnant ponds. 
But by far the moft curious of this genus is the Vorticella 
convallaria ; much refembling cyathina, but cluttered or 
gregarious ; bell-fhaped, with two pair of little arms, 
and a projectile ftem. Thefe vorticellae are popularly 
known by the name of bell-animals; and are generally 
found adhering to fome hard fubftance in the water. 
They are reprefented in the annexed Engraving at fig. 7, 
as found by M. Rofel, attached to a curious cornu am- 
monis , with points projecting from the back. To the 
naked eye this group appeared only as fo many little 
white fpecks; but under the microfcope, as little bells, 
agitating the water to a confiderable diftance. The 
ftems of thefe have a peculiar motion, they draw them, 
felves up and fliorten all at once, taking the form of a 
fpiral ; in a moment after they again refume their for¬ 
mer fhape, ftretching themfelves out ftraight as before. 
Many of them may be feen at times fattened to each 
other by their tails; the cilia, which are two on each 
fide of their mouth, are very feldom to be perceived. 
Trichoda. This genus of invifible worms contains 
fixty fpecies, which like the preceding are claffed in three 
divifions. ift. Thofe which are covered with a foft 
down or hair, as (hown at fig. 8, Trichoda ciliata, kidney, 
fliaped, pale red; found in frefh water: or as at fig. 9, 
Trichoda fulcata, ovate, pointed at the tip, with a groove 
along the abdomen, ciliate on each fide; of a pale-red. 
difh colour; found between the valves of the mytilus 
edulis. Alfo, others of this divifion are exhibited at 
fig. 10, Trichoda transfu^a, broadifli, and pale blue; the 
fore-part hairy, and ciliate behind : and at fig. 11, Tri¬ 
choda inquilinus, in three pofitions, fheathed in a cylindri¬ 
cal bag, with a fmall pedicle within the bag, pale blue, 
and covered with molecules, fuppofed to be the ovaries. 
Both of thefe are found in fea-water after being kept 
(landing two or three days. zdly. Thofe furniflied with 
cirri, and called Himantopus ; exhibited at fig. 12, 
Trichoda acarus, cirrated behind, and (harp before, nearly 
pear-fhaped, and full of black molecules; found in frefh 
waters; yellowilh. 3dly. Thofe which are horned, and 
called Kerona, as reprefented in two pofitions, at fig. 
13, Trichodapullaftcr, body ovate, pale yellow; fore-part 
finuate, with a creft in front; bafe with briftles or fpines; 
ovaries diftirxStly on the body : found in ditches of ftag¬ 
nant water. 
Cercaria. This is a pellucid invifible worm, fur¬ 
niflied with a tail, fometimes ending in two moveable 
fpines. There are thirteen fpecies ; one of which, Cer¬ 
caria podura , is (hown in the Engraving at fig. 14. It is 
a cylindrical taper worm, pale yellow, with opaque 
molecules on the body, and tail cleft: found in the 
ftagnant marfhy waters. 
Bursaria. A very Ample membranaceous hollow 
worm; of whidh there are only three fpecies as yet 
4 Z known. 
