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FIGURE 2 Examples of germ plasm morphology in several invertebrate and vertebrate species used for research about the preformative (maternal inheritance) mechanism of primordial germ cell specification. (A) PGL-1 protein-labeled P-granules in 2-cell C. elegans embryo. Adapted with permission from Spike et al. (2008). (B) Vasa protein-labeled pole plasm in a Drosophila embryo less than 1 h after egg laying, also magnified (B’) to show individual Vasa-positive germ granules that comprise the pole plasm. Adapted from Trcek et al. (2015) and available via CC-BY license. (C) Nasonia vitripennis wasp embryos in division cycle 2–3 and (C’) pre-syncytial blastoderm formation, labeled for the oosome component oskar RNA. Adapted from Lynch et al. (2011) and available via CC-BY license. (D) Vegetal view of germ plasm in albino Xenopus 2-cell and 4-cell (D’) embryos labeled for dazl RNA. Adapted with permission from Houston et al. (1998). (E) Zebrafish 4-cell embryo labeled for nanos RNA to show rod-like germ plasm masses at the cleavage furrow ends, also magnified (E’) to show structure of aggregated nanos germ plasm ribonucleoparticles.