Many cycles may be accomplished from the still cell to the zoospores, and back again, producing numerous generations from the same plant before it returns to the red thick-walled cell, which may again be dormant for an unlimited time. These cycles, however, do not finish the history of the plant, for there can be little doubt that, in some stage of its existence, a conjugation of two cells occurs, as in the Palmoglœa. Sometimes when the division of the endochrome of the spore of the Protococcus is successively divided into sixteen parts, or even sooner, the new cells thus produced get two long cilia, as in fig. 7 H, and are liberated before they acquire their cellulose coat. This motile primordial cell soon acquires a bag-like investment (fig. 7 I, K, L,) of cellulose, through which the cilia pass, and thread-like extensions of the protoplasm are not unfrequently seen to radiate from the primordial cell to the surrounding bag, as in fig. 7 I, showing that the transparent space is only occupied by a watery liquid. The varieties of this plant are very numerous, and all related to one another. Sometimes the whole of the matter within the primordial cell of the spore divides at once into 4, 8, or 16 parts, giving rise to as many minute primordial cells. The cilia are extensions of the colourless transparent film which covers the zoospores, and their vibrations are generally believed to be a consequence of the vital contractibility of that film, and intimately related to the changes taking place in the cell on which they are borne. The persistence of their motions after a cell is detached from a compound body covered with them, being like the persistence of the contractibility of muscle fibre after being detached from a living animal, proves that we must look to a contractile energy in the film of protoplasm for the maintenance of these curious operations. It appears that a cell cannot perform two functions at the same time, and that one must either precede or follow the other. Thus, the zoospores have two distinct periods of action; the first is that of mechanical motion alone, which is followed by one of growth and multiplication, manifestations which, though very dissimilar, are really modes of action of the same vital energy that formed these bodies while they were yet in their parent cell. In fact, it seems to be a general law, that each cell is endowed, altogether or for a time, with its own mode of action, and is incapable of any other.