If the whole history of the zoospores of Peronospora and of Coleochaete were unknown, they would undoubtedly be classed among “Monads” with the same right as Heteromita; why then may not Heteromita be a plant, even though the cycle of forms through which it passes shows no terms quite so complex as those which occur in Peronospora and Coleochaete?  And, in fact, there are some green organisms, in every respect characteristically plants, such as Chlamydomonas, and the common Volvox, or so-called “Globe animalcule,” which run through a cycle of forms of just the same simple character as those of Heteromita.

The name of Chlamydomonas is applied to certain microscopic green bodies, each of which consists of a protoplasmic central substance invested by a structureless sac.  The latter contains cellulose, as in ordinary plants; and the chlorophyll which gives the green colour enables the Chlamydomonas to decompose carbonic acid and fix carbon as they do.  Two long cilia protrude through the cell-wall, and effect the rapid locomotion of this “monad,” which, in all respects except its mobility, is characteristically a plant.  Under ordinary circumstances, the Chlamydomonas multiplies by simple fission, each splitting into two or into four parts, which separate and become independent organisms.  Sometimes, however, the Chlamydomonas divides into eight parts, each of which is provided with four instead of two cilia.  These “zoospores” conjugate in pairs, and give rise to quiescent bodies, which multiply by division, find eventually pass into the active state.

Thus, so far as outward form and the general character of the cycle of modifications, through which the organism passes in the course of its life, are concerned, the resemblance between Chlamydomonas and Heteromita is of the closest description.  And on the face of the matter there is no ground for refusing to admit that Heteromita may be related to Chlamydomonas, as the colourless fungus is to the green alga. Volvox may be compared to a hollow sphere, the wall of which is made up of coherent Chlamydomonads; and which progresses with a rotating motion effected by the paddling of the multitudinous pairs of cilia which project from its surface.  Each Volvox-monad, moreover, possesses a red pigment spot, like the simplest form of eye known among animals.  The methods of fissive multiplication and of conjugation observed in the monads of this locomotive globe are essentially similar to those observed in Chlamydomonas; and, though a hard battle has been fought over it, Volvox is now finally surrendered to the Botanists.