Fig. 29. Paramecium aurelia and its Parasites.
The prodigious number to which the calculation would reach, if we were to add the other modes of propagation, viz., by germs and by budding, we dare not mention: it would only be necessary to place a single germ in a favourable condition for its development, in order to produce myriads of these microscopic animalcules in a very few days.
We have seen three modes of reproduction in the Infusoria; it is possible that a fourth mode exists, to which its partisans give the name of spontaneous generation. According to their views, an infusoria can be produced without egg-germ or pre-existent parent. It would be sufficient to expose organic matter, animal or vegetable, to the action of the air and water at a suitable temperature, in order to see this matter organize itself, and form itself into living infusorial animals.
Such is the general enumeration of the question of spontaneous or heterogeneous generation, on which so much has been written in the last ten years. The great expounders of the doctrine have been the two French naturalists, MM. Pouchet and Joly. Their views have, however, made little progress; they have, on the contrary, met with vigorous opposition from the generality of French naturalists, and from most of the members of the Académie des Sciences of Paris, who have raised their voices against a doctrine which is contrary to the ordinary course of nature. In short, the direct observations made upon the theory of "primitive generation" are as yet wanting in necessary exactness; those observers who profess to have witnessed the sudden origin of the minutest of the infusoria from elementary substances have in all probability overlooked the organic structure of these elementary bodies. The wonderful changes of form undergone by many infusoria have their limits, and the laws governing them have still to be defined. With the poet we may say:
"Grammatici certant et adhuc sub judice lis est."
Many of the Infusoria are subject to metamorphoses, and it has already been ascertained that certain species which have been considered as distinct are only transition forms of the same species depending on age.
We know that it is common for insects to enclose themselves in protecting envelopes, and to remain for whole months shut up in this their retreat, to all appearance dead. Similar facts have been observed in the Infusoria. We have even seen some of these beings surrounding strange bodies as if in a mass of jelly, forming a sort of living envelope around them.
The average duration of life with them is only a few hours; but certain species present, in relation to the duration of life, phenomena which are only imperfectly known, but which never fail to excite the surprise and admiration of the naturalist. By drying certain infusoria with care, it is possible to suspend and indefinitely prolong its life. Thus dried, and covered with a powder, which shelters it from every breath of wind, it may be carried to any given distance, through any indefinite period of time—abandoned on some ledge of rock, on a housetop, in the cleft of a wall, or under the capital of a column; but let a drop of water approach it, and the dormant being awakes immediately—the microscopic Lazarus springs again into existence: feeds and multiplies as before: and its life, suspended possibly for years, resumes its interrupted course!
Into what a world of reflection does not a revelation of this mysterious property of a living creature plunge us!
The physiologist Müller has noted another peculiarity in infusorial life. These animalcules can lose a part of their bodies without being destroyed; the dead part disappears, and the individual, diminished by one-half, or reduced to a fourth of its former size, continues to live as if nothing had happened. Müller has observed a kalpode (Kolpoda meleagris) thus melt before his eyes until scarcely a sixteenth part of its body remained. After its loss, this sixteenth part of an animal continued to swim about without troubling itself as to its diminished proportions. "The infusoria," says Frédol, in "La Monde de la Mer," "present yet another kind of decomposition. If we approach the drop of water in which it swims with the barb of a feather dipped in ammonia, the animalcule is arrested in its movement, but its cils continue to move rapidly. All at once, upon some point of its circumference, a notch is formed, which increases bit by bit until the whole animal is dissolved. If a drop of pure water is added, the decomposition is suddenly stopped, and what remains of the animalcule recommences its swimming movements." (Dujardin.)