Page:Popular Science Monthly Volume 79.djvu/584

580 swarm of gametes found in other Gregarines. Here, also, the internal or "nursed"; condition of the gametes is a new development or adaptation.

Similarly in Paramecium the three divisions of the micronucleus may be interpreted as representing an ancestral brood of conjugating gametes, only two of which are now functional, the one representing a macrogamete or female form, the other a microgamete or male cell. Unlike Ophryocystis, the Paramecium individual does not become a nurse for the conjugating gametes, but remains, as before, the mechanism for the performance of the various physiological activities and the vehicle of the somatic and germ plasms.

The widely accepted view, therefore, as first formulated by Weismann and repeatedly stated in general works on biology, that Protozoa differ from Metazoa in having no equivalent of the somatic cells and therefore no somatic, or natural, death, must be abandoned. In the vast majority of Protozoa there is a clearly defined equivalent of somatic cells and an equivalent of natural death. The conditions in Paramecium and its allies are different from those of other protozoa, the old individual does not die at conjugation but is completely reorganized and built up of parts derived from the product of fertilization exactly as in Metazoa. The protozoon is not a potential germ cell, but like the metazoon is the carrier of the racial germ plasm which, in the great majority of protozoa is differentiated from the somatic plasm. As the germ cells of the metazoon become segregated into a germinal epithelium, becoming functional at maturity, so the germ plasm of the protozoon becomes segregated as chromidia or granules of a specific kind of chromatin, in the cell and is likewise functional at maturity.