Propagation, by division of the body, is not confined to the more simple animalcula ; it extends to those of complicated structure, such as the vorticellee, to which genus the one we have just described probably belongs. The vorticellm are so denominated, from their power of creating a vortex in the fluid which they inhabit, by means of a circular row of fibrilli, proceeding from the head or anterior periocI; and the floating particles in the infusion, being absorbed, the animal can select its food from among them.
The vorticelloe hiani propagates by a longitudinal di vision of the body. The figure of this animal resembles a ball, to which a filament or tail is attached. Previous to the commencement of division, the anterior part ap pears languid, then a small cleft is seen in it, which gradually encreasing, each portion exhibits a mishapen animalcula. As the separation advances, the figure of each oecomes more perfect, the division is at length completed, and both become entire, and well-formed animals. The filament, however, belongs only to one, the other acquires it. When the division is almost perfected, each part forms its own peculiar vortex, in points diametrically opposite.
Several of the vorticeilx resemble a plant in minia ture, consisting of a stein, that puts forth numerous branches and twigs, each terminated by a bell in its fi brille, which forms the active part of the animal. Of this kind are the racemosa, pyraria, convallaria, polypina, and acinosa. Every bell, with its filament and fibriili, has a spontaneous motion, independent of the rest ; by alternate contraction, and extension, it can approach and recede from the stalk, or branches. Sometimes the whole will instantaneously close into a minute, round, white speck, at the root where it fixes, and as instan taneously expand into a perfect tree. The common stem may be detached at pleasure, and then the entire animal swims through the fluid, with its numerous fila ments, bells, or fibrilli, often exceeding an hundred, in motion ; each forming its own peculiar vortex to absorb its food ; and thus presenting a singular and interesting spectacle, of which it is difficult to convey an adequate idea by description.
If a bell, with its filament or pedicle, is detached from the stalk, the pedicle fixes to another place, and a new race of animalcula is produced. Then the vorticellx ra
mosx fixed in this manner, -eight new bells germinate from the root of the old one, which in a few hours rise on their own pellicles ; and from those bells others, in a short time, also proceed. But it likewise appears, that the twigs, six days after losin4 the bells, renew them at their extremities.
The vorticellee pyraria is also of a similar structure ; it resembles a shrub, with numerous ramifications, each terminated by an anirnalcula. During the progress of propagation, two animalcula are found at the extremity, instead of one ; or, if any appear single, they are mark ed with a slight furrow, which indicates incipient divi sion. Each produces two, then four, eight, sixteen, and thirty-two, animalcula. Spallanzani describes his ob servations on one of these vorticellx. It resembled 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 extremity. Every three or four se conds, the trunk unexpectedly contracted towards the base, and instantaneously drew in all the branches, twigs, and animalcula, but in a moment restored the tree complete, with all its animals, to the original state. During the course of an observation, the ramifications of the plant had so much extended, and the numbers of the animalcula encreased, that its circumference was tripled. But the supervening death of the animalcula 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 vibration of the fibrilli, or the attending vor tex ; each animalcula became disfigured, and was de stroycd. The plant lived while the animalcula formed a part of it ; after that, its vegetation was at an end, its motion ceased, and death ensued.
There is one species of animalcula sometimes found in an infusion of beets, which propagates by a small fragment detaching itself obliquely from the body. This, when separation is accomplished, is not a twelfth part of the original in size ; yet it. swims actively through its fluid, and in the course of a day becomes equal to its parent, when it begins to propagate in the same manner.