Fig. 5.

Central core and fluid dynamics. a The central core in S. papillosus dissected female gonads visualized by staining against α-tubulin (green) and DAPI (blue). Panel 1 shows no visible central canal in the distal gonad (with the giant nuclei) when stained with α-tubulin (top), but a clearly visible canal in panel 2 (outlined in white) starting just before the gonadal loop (beginning of the band of small nuclei). Bottom panels show merge with DAPI. b Differential interference contrast (DIC) time-lapse images of an injection experiment using mineral oil in a P. trichosuri adult female gonad, showing the rapid movement and incorporation of an oil droplet (if injected into the central core) proximally into growing oocytes. The gonad arm is outlined in yellow, the oil drop in red, developing oocytes are labeled and outlined in white dashes, the spermatheca (Sp.) is in blue, embryos labeled in the uterus outlined with green. Soon after injection, the single large oil drop is broken into smaller droplets, which quickly move proximally past the gonadal loop (seen in the left most image marked as the oil drop, at 5 min post-injection). Once proximal, the oil droplets move further down into developing oocytes (seen in the middle image at 20 min post-injection) to finally become incorporated within them (seen in the right most image, 1 h post-injection)