Page:EB1911 - Volume 23.djvu/264

Rh distinct periods in the life cycle which we may call A and B; the individuals of the A period being distinguished by the presence of radiating spicules of MgCO3 in the gelatinous theca; the resolution of period A is simple (fig. 5, 3) and the uninucleate

brood-cells are amoebulae (pseudopodiospores) (fig. 5, 4) which grow into the multinucleate B type, with a nonspiculate theca (fig. 5, 5). The resolution of the B type is preceded by rapid multiplication of the nuclei by mitosis (fig. 5, 7), and the uninucleate cells are 2-flagellate zoospores (fig. 5, 9). These pair with zoospores of a different brood to their own (fig. 5, 10) (i.e. they are exogamous gametes); and the fusion cell (fig. 5, 11) so formed is the starting-point of the A type (fig. 5, 12). Brood formation by resolution of a multinucleate individual has been observed or conjectured in Amoeba, &c.

A formation of numerous pseudopodiospores within Pelomyxa has been repeatedly described, and these have been seen to conjugate equally, the zygote becoming multinuclear. But the possibility of the alleged reproductive cells being parasites has not yet been fully excluded.

Chlamydophrys stercorea is a small Filose, occurring in the faeces of several mammals, but only forming its characteristic shell outside the body; plastogamic monstrosities are frequent. The nucleus degenerates, and is expelled with some plasm. The chromidia remain inside the shell, and differentiate or aggregate into about eight nuclei; the cell is then resolved into as many 2-flagellate swarmers, which escape as isogamous exogametes. The zygote becomes surrounded by a brown cyst. When