Page:Littell's Living Age - Volume 128.djvu/658

648  is of common occurrence among the lowest plants and animals, and is known as a contractile vacuole.

The little creature thus described sometimes propelled itself with great activity, with a curious rolling motion, by the lashing of the front cilium, while the second cilium trailed behind; sometimes it anchored itself by the hinder cilium and was spun round by the working of the other, its motions resembling those of an anchor buoy in a heavy sea. Sometimes, when two were in full career towards one another, each would appear dexterously to get out of the other's way; sometimes a crowd would assemble and jostle one another, with as much semblance of individual effort as a spectator on the Grands Mulets might observe with a telescope among the specks representing men in the valley of Chamounix.

The spectacle, though always surprising, was not new to me. So my reply to the question put to me was, that these organisms were what biologists call monads, and though they might be animals, it was also possible that they might, like the Bacteria, be plants. My friend received my verdict with an expression which showed a sad want of respect for authority. He would as soon believe that a sheep was a plant. Naturally piqued by this want of faith, I have thought a good deal over the matter; and as I still rest in the lame conclusion I originally expressed, and must even now confess that I cannot certainly say whether this creature is an animal or a plant, I think it may be well to state the grounds of my hesitation at length. But, in the first place, in order that I may conveniently distinguish this "monad" from the multitude of other things which go by the same designation, I must give it a name of its own. I think (though for reasons which need not be stated at present, I am not quite sure) that it is identical with the species Monas lens, as defined by the eminent French microscopist Dujardin, though his magnifying power was probably insufficient to enable him to see that it is curiously like a much larger form of monad which he has named Heteromita. I shall, therefore, call it not Monas, but Heteromita lens.

I have been unable to devote to my Heteromita the prolonged study needful to work out its whole history, which would involve weeks, or it may be months of unremitting attention. But I the less regret this circumstance, as some remarkable observations recently published by Messrs. Dallinger and Drysdale on certain monads, relate, in part, to a form so similar to my Heteromita lens, that the history of the one may be used to illustrate that of the other. These most patient and painstaking observers, who employed the highest attainable powers of the microscope and, relieving one another, kept watch day and night over the same individual monads, have been enabled to trace out the whole history of their Heteromita; which they found in infusions of the heads of fishes of the cod tribe.

Of the four monads described and figured by these investigators one, as I have said, very closely resembles Heteromita lens in every particular, except that it has a separately distinguishable central particle or "nucleus," which is not certainly to be made out in Heteromita lens; and that nothing is said by Messrs. Dallinger and Drysdale of the existence of a contractile vacuole in this monad, though they describe it in another.

Their Heteromita, however, multiplied rapidly by fission. Sometimes a transverse constriction appeared; the hinder half developed a new cilium, and the hinder cilium gradually split from its base to its free end, until it was divided into two; a process which, considering the fact that this fine filament cannot be much more than .00001 of an inch in diameter, is wonderful enough. The constriction of the body extended inwards until the two portions were united by a narrow isthmus; finally they separated, and each swam away by itself, a complete Heteromita, provided with its two cilia. Sometimes the constriction took a longitudinal direction, with the same ultimate result. In each case the process occupied not more than six or seven minutes. At this rate, a single Heteromita would give rise to a thousand like itself in the course of an hour, to about a million in two hours, and to a number greater than the generally assumed number of human beings now living in the world in three hours; or, if we give each Heteromita an hour's enjoyment of individual existence, the same result will be obtained in about a day. The apparent suddenness of the appearance of multitudes of such organisms as these in any nutritive fluid to which one obtains access, is thus easily explained.

During these processes of multiplication