Fig. 1: Mechanical immobilisation of L1 larvae.

a Synchronised 4.5-h-old L1 larvae right after they were added with MPEG on a triangular agarose pad. b L1 larvae at the end of MPEG evaporation (concentric rings represent precipitated salts). c L1 larvae after the addition and partial evaporation of polystyrene microspheres. d L1 larvae after positioning the coverglass (the ring around larvae consists of precipitated microspheres and surfactant). e Detailed view of L1 larvae immobilised under the coverglass. The panel shows the ideal condition with almost no contact between animals. f Cartoon of the mount. The triangular pad is surrounded by mineral oil and surmounted by a 1½ coverglass. Vaseline is added only at the four corners of the coverglass. g Transverse cross-section of the mount. The coverglass presses L1 larvae against the agarose pad, causing mild compression of specimens (elliptic cross-section, left-right diameter is 20 μm or so) and the formation of concavities at the L1 cuticle-agar pad interface (visible also in (e)). In this condition, the microspheres between the L1 cuticle and the agar pad generate strong friction. Only the animal on the left faces the coverglass with its left side, QL.p is very close to the coverglass, and its division can be recorded in super-resolution. h Frontal cross-section of an immobilised L1 larva. The high content in agarose makes the pad deform mildly and allows perfect adhesion of the worm cuticle along the entire anterior-posterior axes. Microspheres are omitted to simplify the cartoon. Only (a, d) images are from the same replicate. a–e The small inserts at the lower right-hand side corners show the field-of-view (red boxes) relative to the triangular pad. Air bubbles in (a, d) are within the agarose pad and do not cause discontinuity to the surface.