stem may be detached at pleasure, and then the 
entire animal swims through the fluid, with its 
numerous filaments, bells, or fibrilli—often ex- 
ceeding an hundred—in motion; each forming 
its own peculiar vortex to absorb its food: thus 
presenting a singular and interesting spectacle, 
of which it is difficult to convey an adequate idea 
by description. The Vorétvcella pyraria, Fig. 5, 
resembles a shrub, with numerous ramifications, 
each terminated by an animalcule. During the 
progress of propagation, two animalcules are 
found at the extremity, instead of one; or, if 
any appear single, they are marked with a slight 
furrow which indicates incipient division. Each 
produces two, then four, eight, sixteen, and thir- 
ty-twoanimalcules. Spallanzani describes his ob- 
servations on one of these Vorticelle. It resem- 
bled a tree in miniature; numberless branches 
dividing into smaller ones, proceeded from the 
trunk ; these divided into others successively less, 
and each of the smaller bore a bell at the extrem- 
ity. Every three or four seconds, the trunk un- 
expectedly contracted towards the base, and in- 
stantaneously drew in all the branches, twigs, 
and animalcules, but in a moment restored the 
tree complete, with all its animals, to the origi- 
nal state. During the course of an observation, 
the ramifications of the plant had so much ex- 
tended, and the numbers of the animalcules so 
much increased, that its circumference was tri- 
pled: but the supervening death of the animal- 
cules occasioned that of the plant. They began 
to fall from the branches, as fruit falls from the 
tree, and, as they gradually separated, the motive 
power finally was lost. Spontaneous extension 
and contraction were no longer seen; the vibra- 
tion of the fibrilli, or the attending vortex ; each 
animalcule became disfigured and was destroyed. 
The plant lived while the animalcule formed a 
part of it; after that its vegetation was at an 
end, its motion ceased, and death ensued. 
The Volvoxr globator, Fig. 7, is a globular ani- 
malcule, of a greenish colour, visible by the 
naked eye. It is frequently found in the water 
of ditches, and marshes abounding with growing 
vegetables, as well as in those in a decomposing 
state, and often in considerable numbers. Its 
mode of progression through the fluid is by re- 
volving on itself, or rolling like a sphere ; whence 
its name has beenderived. This animalcule con- 
sists of extremely transparent membranaceous 
substances, containing minute globules, irregu- 
larly dispersed within it. On examination with 
a very powerful magnifier, the globules appear 
so many young Volvoxés, each provided with its 
diaphanous membrane, and within that again is 
involved another race of descendants. When the 
Volvoxes have attained a certain maturity, the 
included young begin to move, detach themselves 
from the parent, and, successively escaping from 
the investing substance, swim about in the in- 
fusion. When all have left it, the common en- 
velop, or mother, becomes motionless, bursts, and 
ANIMALCULE. 
disappears. Then the new volvoxes rapidly in- 
crease in size; their included globules likewise 
grow, they begin to move, the parent bursts, and 
the young swim at large in the infusion. By 
isolating these animals in watch-glasses, the thir- 
teenth successive generation, from a single parent, 
has been obtained. 
Such are some of the more remarkable methods 
by which the race of those minute animals is per- 
petuated. But the dangers to which they are 
exposed infinitely exceed those attendant on the 
larger animals, not only from the noxious quality 
imparted to infusions, but from evaporation, which 
is destructive to myriads beyond the power of cal- 
culation to reach. Independent of those that die 
in giving existence to their young, they are, like 
other animals, subject to instantaneous death. 
According to Muller, several of the larger species 
are destroyed and totally dissolved by simple con- 
tact with the air. Some he has seen decomposed 
on approaching the edge of a drop; and others, 
amidst the rapidity of their course, have been 
dissolved in a moment. Too much heat and cold 
are alike fatal to them: they die at a degree of 
heat between 106° and 111°; and if the liquid 
which they inhabit freezes, it kills them. But if 
by any means its fluidity can be preserved, they 
will not be destroyed below the cold of 12°, or 
even 20°, under the freezing point. The Anguil- 
le of vinegar can endure a still greater degree 
of cold. Dr. Power remarks, that the vinegar 
may be frozen and thawed several times, and 
they will still be as lively as ever. 
But some animalcules seem to enjoy a privilege 
denied to the rest of the animated creation: they 
can be revived after death. So singular and unac- 
countable a property merits the deepest consider- 
ation. Nor is this wonderful prerogative confined 
to the momentary interruption of life: it suc- 
ceeds—so far as we hitherto know—though the 
vital functions have been suspended for an un- 
limited length of time. In recurring to analo- 
gies, we find, that there are many animals, quad- 
rupeds, serpents, and chiefly of all insects, which 
are reduced to a state of torpidity by the simple 
approach of cold, without any other operative 
cause: their motion ceases, their members stiff- 
en, and they are absorbed in a profound sleep, 
from which they can be aroused by the applica- 
tion of heat alone. But this lethargic state is 
widely different from that of death, though that 
will be its termination if too long protracted. 
Perhaps this may also be the case with those 
animalcules of which we treat; and if the state 
into which they are brought be not real and ab- 
solute death, in the most rigorous sense of the 
word, or that which allows the animal substance 
to decompose, too long suspension of the vital 
functions, without renewing them by resurrec- 
tion, may be alike fatal in its consequences. The 
Wheel-animal, or Vorticella rotatoria | Figs. 8 and 
9], of systematic authors, is one of the animalcules 
enjoying this admirable prerogative in the most 
N 
a a rn 
