(A) Along the oral-aboral axis, adult Nematostella can be regionally subdivided into the disc (mouth and tentacle base), capitulum (pharynx), scapus (gametogenic region) and physa (non-gametogenic region; Williams, 1975). (B–E’) Female and male cross sections were immunolabeled with Vas2 (red) and counter-stained for nuclei (green). PGC-like cells (arrows in B–B’ and C’) localize next to the maturing oocytes and sperm stem cells (spermatogonia, arrowheads in C–C’), which divide and give rise to sperm in the sperm cyst lumen. Note there are Vas2 puncta surrounding the nuclei of spermatogonia. (D–E’) PGC-like cells also localize aborally in the physa, the site of occasional asexual fission (Hand and Uhlinger, 1995; Burton and Finnerty, 2009). Aboral migration may thus ensure fertility in asexually-produced progeny. (F) Schematic diagrams depict the cross-sectional localization of PGC-like cells (red) in adult mesenteries. The boundaries of mesentery are delineated by gray lines. Scale bar = 50 µm in B; 100 µm in C, D, and E; 20 µm in B’, C’, D’, and E’.