The germ plasm (or polar plasm) is a zone found in the cytoplasm of the egg cells of some model organisms (such as Caenorhabditis elegans, Drosophila melanogaster, Xenopus laevis), which contains determinants that will give rise to the germ cell lineage. As the zygote undergoes mitotic divisions the germ plasm is ultimately restricted to a few cells of the embryo, these germ cells then migrate to the gonads.

The German biologist August Weismann formulated the now discredited germ plasm theory in the 1890s, in which he stated that the germ plasm was the essential nuclear part of germ cells, that it remained qualitatively unchanged from the zygote (in contrast with somatic cells) and was responsible for heredity.

See August Weismann and his Germ Plasm TheoryThe German biologist August Weismann (b.1934-d.1914) formulated the now defunct germ plasm theory in 1883, in which he stated that the germ plasm was the essential nuclear part of germ cells, that it remained qualitatively unchanged from the zygote (in contrast with somatic cells) and was responsible for heredity. In other words it states that a genes determination was sealed as it, and each of it's progeny received fewer and fewer genes from what he called the "germ plasm." (That there is only a set "amount" of "germ plasm" (what we know as genes) and that it was gradually divided amongst the offspring). Cases such as Dolly (the famous cloned ewe) which, via somatic cell nuclear transfer, proved that adult cells retain a complete--as opposed to Weissman's increasingly determined gradual loss of genetic information--set of information; finally putting Weismann's theory to rest.