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Figure 1 | EvoDevo

Figure 1

From: Early embryonic determination of the sexual dimorphism in segment number in geophilomorph centipedes

Figure 1

Strigamia embryonic and post-embryonic stages used for leg-bearing segment counting and sex determination. (A) Lateral view of an early Stage 6 embryo, live in mineral oil: lateral illumination and black background allow segment counting (45 leg-bearing segments (LBSs) in this specimen, see insert). (B) An early Stage 6 flat-mounted germ band, stained with DAPI (4,6-diamidino-2-phenylindole) to highlight the morphology. The stage of this specimen corresponds to that of the embryo shown in (A) and is characterised by the lateral spreading of the germ band in its middle portion. This specimen has 43 LBSs; the 44th LBS here begins to appear, but would not be visible in the live embryo. (C), (D), (E) Adolescens I stage: (C) live specimen in mineral oil, lateral view; (D), (E) high magnification of the ventral side of the terminal trunk mounted on a slide and viewed at the compound microscope with Nomarski optics. This is the first stage at which it is possible to determine the sex because of the sexual differentiation of the genital sternite (arrowhead), with lateral protrusions in males (D) and rounded in females (E). At this stage, the legs of the last LBS are already distinct, notably by the swollen coxopleuron, but they are not obviously different in males and females. (F), (G) Final differentiation between live adult male and female: in the studied population, the modal number of LBSs in males is 47 (F) and in females is 49 (G). By this stage the last pair of legs are highly modified in the male, swollen and bearing sensory and glandular structures (F,F1). (F), (G) dorsal view; (F1), (G1) ventral magnified view of, respectively, (F) and (G). a, antenna; p, proctodeum.*Artefactual rupture of the germ band. Scale bar: (A), (B) 300 μm; (C) 1mm; (D), (E) 100 μm; (F), (G) 1 mm; (F1), (G1) 300 μm.

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