Expression of the engrailed gene in the embryo of the millipede Glomeris marginata. Shown is the localisation of engrailed transcripts via in situ hybridisation. The embryo proper is located on the surface of a large yolk mass that is consumed as the embryo develops. In the stages shown, the yolk mass is still very large, so that the embryo proper is still open dorsally. This is the reason why the future dorsal tissue is still located "laterally", i.e. next to the ventral tissue (indicated in the figures). This will change in very late stages, when the yolk is consumed entirely and the "lateral" portions of the germ band fuse dorsally (dorsal closure). The ventral engrailed expression marks the posterior part of the ventral segmental units. The ventral stripes are marked with p,1,2,3,4,5,6,7. Dorsally, the engrailed transcripts are in stripes (asterisks) localised at a different intrasegmental position as on the ventral side. The dorsal stripe of engrailed expression is not associated with any morphological structure at this stage, but is in the middle of the dorsal metameric units, which also becomes obvious if one compares with figure 7 B and D. The location of the future ventral and dorsal tissue is marked (dorsal-ventral-dorsal or d-v-d). Note that the dorsal tissue is on the lateral part on both sides of the germ band at this stage; during dorsal closure these tissues fuse on the dorsal side to give rise to one dorsal tissue. The head segments are marked in the embryo in panel D, for details we refer to [4,6]. (A and B): embryo at stage 4.1, (C and D): embryo at stage 5 (staging see [4,6]). Panel A and C show the bright field micrograph of the in situ hybridisation staining; panel B and D show the epifluorescence image of the embryo in A and C, respectively, in which the nuclear DAPI staining becomes bright, and the in situ hybridisation staining appears dark due to quenching of the fluorescence. Abbreviations: d: dorsal; v: ventral; lb: labrum; oc: ocular segment; an: antennal segment; pmd: pre-mandibular segment; md: mandibular segment; mx: maxillary segment; p: post-maxillary segment; 1–7: ventral leg bearing segment 1–7.