The volvox globator is a globular animalcula, of a greenish colour, visible by the naked eye. It is fre quently found in the water or ditches, and marshes abounding with glowing vegetables, as well as those in a decomposing state, and often in considerable num bers. Its mode of progression through the fluid is by revolving on itself; or rolling like a sphere, whence its name has been derived. This animalcula consists of extremely transparent membranaceous substances, con taining minute globules, irregularly dispersed within it. On examination with a very powerful magnifier, the globules appear so many young volvoxes, each pro vided with its diaphanous membrane, and within that again is involved another race of descendants. Some observers have discovered even down to the fifth gene ration in the parent ; others have not been able to see farther than the third. When the volvoxes have attain ed a certain maturity, the included young begin to move ; they detach themselves from the parent, and, successively escaping from the investing substance, swim about in the infusion. When all have left it, the common envelope, or mother, becomes motionless, bursts, and disappears. Then the new volvoxes rapidly encrcase 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 ani-' mals in watch glasses, the thirteenth successive gene ration, from a single parent, has been obtained.
The monas uva is an animalcula resembling a cluster of several minute corpuscules joined together, being sometimes four or five in number, and even more. Its propagation is effected by each corpuscule detaching it self from the groupe, and transforming into a new clus ter, which in time divides as it were into 'pieces, for the purpose of perpetuating the race.
The gonium pectorale is a greenish animalcula, con sisting of sixteen oval corpuscules, all invested by a common membrane. While at rest, they exhibit a sphe rical shape, when in motion an elliptical one ; but the figure of the whole animal is quadrangular. This ani malcula propagates by the bursting of the membrane; the parent thus dying in giving birth to sixteen young. each of which, in its turn, in like manner produces six teen descendants.
Analogous to these is another infusion animalcule. which is visible by the naked eye ; but we are unable to ascertain the precise genus to which it belongs, though most probably it is the volvox splarula of Muller. This animal dwells at the bottom of infusions of the marsh lentil. It is of a globular figure, and appears com pletely covered by tumours ; these, however, are so many concentric strata, not of tumours, but of animal cula, all aggregated above each other. The animalcula, or parts forming the first stratum, separate from the sphere, and swim about in the infusion, by which means thq second stratum, composed of similar tumours, oT animalcula, is laid open. These also separate, when all the first have departed, and expose a third to view. This also vanishes; so that a fourth and fifth stratum, and even more, make their successive appearance and departure, until the entire globe, from the circumfer ence to the centre, is completely decompoaid into a swarm of minute animalcula. The parent sphere con
sists of at least one hundred parts ; and though its only progressive motion is rolling at the bottom of the fluid, the animalcula detached, swim with the utmost velocity. it one of these young is confined in a watch, it is ob served to attain its full size in a few days, its motion re laxes as its growth encreases, and it ends in the rolling progression. At first the external surface is smooth, it then becomes unequal and covered with tumours, which are the animalcula that at length separate and swim about in the liquid.
Such are some of the more remarkable methods by which the race of those minute animals is perpetuated. 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, an indispensible occurrence in natural events, which is destructive to myriads, beyond the power of calculation to reach. Independent of those that die in giving existence to their young, they are, like other animals, subject to instantaneous death. Ac cording to Muller, several of the larger species are de stroyed and totally dissolved by simple contact 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 de gree of heat between 106° and 11 I° ; 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 de stroyed below the cold of 12°, or even 20°, under the freezing point. The anguillm of vinegar can endure a still greater degree of cold. Dr Power remarks, that the vinegar may be frozen and thawed several times, znd they will still be as lively as ever.
But some animalcula enjoy a privilege denied to the rest of the animated creation. They can be revived after death. So singular and unaccountable a property merits the deepest consideration. Nor is this wonder ful prerogative confined to the momentary interruption of life : it succeeds, so far as we hitherto know, though the vital functions have been suspended for an unlimit ed length of time. In recurring to analogies, we find, that there are many animals, quadrupeds, 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 mem bers stiffen, and they are absorbed in a profound sleep, from which they can be aroused by the application 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 animalcula of which we treat ; and if the state into which they are brought be not real and absolute death, in the most rigorous sense of the word, that which allows the animal substance to decompose, too long suspension of the vital functions, without re newing them by resurrection, may be alike fatal in its consequences.