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distinguished degree. It was first discovered by 
Leeuwenhoek, in 1702, and has since been fre- 
quently the subject of observation by other natu- 
ralists, from whose investigation it appears that 
the singular faculty of resuscitation is extended 
to several species of this animal. It is difficult 
to describe this animal while living, from its per- 
petual change of shape. Sometimes it is protracted 
into extreme slenderness; then it is inflated into a 
short, corpulent figure; one half of the organs com- 
posing the whole will next be concealed, while the 
other is seen in its full size and figure. The Wheel- 
animal fixes itself by means of a point at the one 
extremity or tail, which, if viewed by a power- 
ful magnifier, is found to consist of a number of 
smaller points: and from the other extremity 
or head two organs proceed, resembling wheels, 
which, by a rapid motion that they are suscep- 
tible of, produce a vortex in the surrounding 
fluid. These organs are not exactly of the same 
description in all Wheel-animals: in some they 
are circular, in others semicircular, or even of a 
more irregular figure. Filaments, or fibrilli, of 
various length, according to the different species, 
proceed from them, similar to those that we have 
already said occasion a vortex, for the purpose of 
supplying animalcules with their food. Accord- 
ing to the opinion of several of the most acute ob- 
servers—among whom is Leeuwenhoek—the vor- 
tex is produced by the actual revolution of these 
organs, as of two mechanical wheels ; and they 
describe this revolution as not always proceeding 
in the same direction, but first from right to left, 
then from left to right, and so on alternately. 
When the water containing the Wheel-animal 
evaporates, it becomes languid and inactive, the 
motion of the wheels is interrupted, they are re- 
tracted within the body, the tail loses its hold, 
the shape alters, and the animal dies. Its figure 
is now so small and distorted, that it cannot be 
recognised for the same being. It grows dry and 
hard, and on being touched with the point of a 
needle flies into a thousand pieces. Yet, not- 
withstanding so great an alteration has taken 
place, the animal may still be revived, though kept 
in this condition days, months, and even years, 
without interruption. All that is required for 
its resurrection is its being moistened with water. 
The period of humectation necessary to the re- 
covery of the full and active principle of life is 
various, according to the species of the animal, 
and perhaps the circumstances in which it is 
found. Some revive in a few minutes, others re- 
quire half-an-hour or more. Leeuwenhoek re- 
lates, that when he affused water on a quantity 
of sand that had been dry thirteen days, one ani- 
malcule attempted to swim in five minutes, but 
others not till after the lapse of three hours. It 
has been said, that those dry for years revive as 
soon as those that have been dry only a few hours. 
The precursors of animation consist in the hard 
and disfigured substance beginning to swell; a 
point appears at one extremity, which moves, 
ANIMALCULE. 
with alternate extension and contraction; the 
opposite part also becomes pointed: these are the 
head and tail. The rest of the organs succes- 
sively unfold; the wheels are displayed; the ani- 
mal resumes its original shape, and swims viva- 
ciously through the fluid. The length of time 
during which Wheel-animals may be preserved 
in their quiescent state, and still retain the fac- 
ulty of resurrection, has not hitherto been ascer- 
tained, Leeuwenhoek kept them dry twenty-one 
months, yet they recovered on new humectation. 
Baker revived them after a longer period. Fon- 
tana preserved them two years; and Spallanzani 
seems to infer, that he kept a quantity of sand 
containing these animals four years in a phial, 
and whenever a portion of it was moistened they 
revived. 
There is another animalcule, which is known to 
enjoy the privilege of resurrection in a degree no | 
less eminent than that of the rest ; and, consider- 
ing the place where it is most abundantly found, 
its nature may perhaps be considered even more 
extraordinary than theirs. The external appear- 
ance of a grain of blighted corn resembles soot, 
and its internal substance consists of a dry whit- 
ish matter, which examination with the micro- 
scope exhibits as an aggregate of linear corpus- 
cula intricately interwoven together. Mr. Need- 
ham, in the course of a microscopical observation, 
having moistened this substance for the purpose 
of unravelling it, was agreeably surprised to see 
it immediately testify signs of animation, and the 
dry shrivelled corpuscula afterwards expand into 
so many lively active eels. Many naturalists have 
repeated his experiments, and established a num- 
ber of interesting facts. If the fluid containing 
the eels evaporates, they gradually become life- 
less; when totally gone, their motion has ceased. 
Unlike the other resurgent animals, they have 
not the prudence to forsake places where the water 
dries; but continue attached to the same spot 
without attempting to escape. On the fluid being 
restored, reanimation ensues, first beginning with 
gentle oscillations, then with writhing and con- 
tortion, and, lastly, with the full attainment of 
lively action, But it is to be remarked that 
these animals have no progressive motion; they 
neither rise in the water, nor crawl along the 
sides of the vessel containing them: hence they 
are always found at the bottom, appearing like a 
pellicle, lighter or darker, according to their num- 
bers. The time of immersion required for their 
revival is various: some recover in three hours, 
or less. 
not less than forty hours; and, in certain cases, 
whole days are necessary. Resurrection is accel- 
erated by heat, and retarded by cold. Speaking 
of these animals, Spallanzani observes, that the 
oftener humectation is repeated there will be the 
fewer resurgents. “I had a number of lively eels 
in a watch-glass, the first time they were revived. 
One thousandth part did not recover the eleventh 
time; and the seventeenth there was not one.” 
Baker quotes an instance where it was 
ay 
