Figure 4

Cell division pattern of the mandibular region E(0) on the basis of a 4D-analysis. (A-D) Sequence of the early embryonic development with focus on cell lineage in region E(0) created with SIMI°BioCell. Each genealogical row is color coded. The strict cell divisions are marked by white lines. (E) Scheme of the cell division pattern in the region E(0). The color code and the labeling are the same as in the SIMI°BioCell-reconstruction. The median (midline) region is colored gray. Top: Time point of first visible row arrangement (E(1)) in post-naupliar germ band. At this time the prospective mandibular segment consists of two cell rows (E(0)a and E(0)p) of about 10–12 cells each. Roman numerals indicate the different areas in the mandibular segment. The horizontal line between E(0)p and E(1) marks the genealogical border between these rows, the segmental boundary between the mandibular segment and the segment of the first maxilla, and the border between the naupliar and the post-naupliar regions of the germ band. (F) Photo composition of mandibular cell lineage pattern and SEM picture found in Orchestia. The embryo of the SEM picture is about one cell division cycle in advance. However, at this developmental stage the naupliar segments (antenna 1, antenna 2 and mandible) have small appendage buds, whereas the adjacent posterior region shows only its segmental appearance. The substantial participation of row E(0)aa, E(0)ap and E(0)p in the outgrowth of the mandibular bud is visible.