The ultrastructure of the dorsal body surface epidermal cell junctions in embryonic stages of P. scaber A–E samples of mid-stage embryos A the external morphology of mid-stage embryo S13 B semithin section of an S13 embryo: Epidermal cells on the dorsal part of the body are flattened C in mid-stage embryos S10, an AJ is evidenced between neighbouring epidermal cells. Septa of SJs are not observed D mid-stage embryos S13: the AJ is located subapically and its ultrastructure is similar to that in adult AJs. A short array of septa is evident just beneath the AJ E mid-stage embryos S14: A discontinuous SJ containing short arrays of septa F–I samples of late-stage embryos F late-stage embryo S16 G semithin section of S16 embryo: Epidermal cells of dorsal body surface are flattened H, I in late-stage embryos S16 (H) and S18 (I) SJs are mainly discontinuous and consist of short arrays of septa. Abbreviations: AJ: adherens junction; AM: apical membrane; CU: cuticle; E: epidermis; PCM: precuticular matrix; SJ: septate junction; VM: vitelline membrane. Scale bars: 0,2 mm (A, F); 20 µm (B, G); 200 nm (C, D); 500 nm (E, H, I).