Thus there is really no reason why Heteromita may not be a plant; and this conclusion would be very satisfactory, if it were not equally easy to show that there is really no reason why it should not be an animal.  For there are numerous organisms presenting the closest resemblance to Heteromita, and, like it, grouped under the general name of “Monads,” which, nevertheless, can be observed to take in solid nutriment, and which, therefore, have a virtual, if not an actual, mouth and digestive cavity, and thus come under Cuvier’s definition of an animal.  Numerous forms of such animals have been described by Ehrenberg, Dujardin, H. James Clark, and other writers on the Infusoria.  Indeed, in another infusion of hay in which my Heteromita lens occurred, there were innumerable such infusorial animalcules belonging to the well-known species Colpoda cucullus.[6]

[Footnote 6:  Excellently described by Stein, almost all of whose statements I have verified.]

Full-sized specimens of this animalcule attain a length of between 1/300 or 1/400 of an inch, so that it may have ten times the length and a thousand times the mass of a Heteromita.  In shape, it is not altogether unlike Heteromita.  The small end, however, is not produced into one long cilium, but the general surface of the body is covered with small actively vibrating ciliary organs, which are only longest at the small end.  At the point which answers to that from which the two cilia arise in Heteromita, there is a conical depression, the mouth; and, in young specimens, a tapering filament, which reminds one of the posterior cilium of Heteromita, projects from this region.

The body consists of a soft granular protoplasmic substance, the middle of which is occupied by a large oval mass called the “nucleus”; while, at its hinder end, is a “contractile vacuole,” conspicuous by its regular rhythmic appearances and disappearances.  Obviously, although the Colpoda is not a monad, it differs from one only in subordinate details.  Moreover, under certain conditions, it becomes quiescent, incloses itself in a delicate case or cyst, and then divides into two, four, or more portions, which are eventually set free and swim about as active Colpodoe.

But this creature is an unmistakable animal, and full-sized Colpodoe may be fed as easily as one feeds chickens.  It is only needful to diffuse very finely ground carmine through the water in which they live, and, in a very short time, the bodies of the Colpodoe are stuffed with the deeply-coloured granules of the pigment.