Figure 1. Development and pattern of neuroblasts.

(A) On the left is a schematic drawing of a cross section of the embryonic nervous system of the cricket. This is one of the first depictions of neural lineages, consisting of NBs and stacks of GMCs and neurons (from¹). In the center is a drawing by M. Bate², depicting the full set of NBs in one hemisegment of the grasshopper embryo. The drawing on the right (from³) shows the NB pattern of several hemisegments of the Drosophila embryo, drawn to the same scale. Only S1/S2 NBs, forming four rows and three columns, have formed at the stage depicted. (B) Histological cross sections of the Drosophila embryo prior to (upper panel) and after (lower panel) NB delamination. Only left ventral quadrant of the embryo is shown. The ventral neurectoderm can be distinguished from the dorsal ectoderm by its tall cylindrical cells. Prior to NB delamination, a division in medial column, intermediate column, and lateral column (mVN, iVN, lVN) is evident. (C) Lateral view of Drosophila embryo prior to (upper panel) and after (lower panel) NB delamination. In this and all other figures, anterior is to the left, dorsal is up. Neurectoderm and dorsal ectoderm are shaded in purple, and blue, respectively; white lines and letters indicate segments. (D) NB map of one abdominal hemisegment (from⁴). Left: S1 NBs; locations where S2 and S3 will appear are indicated by filled and open circles, respectively. Center: S1-S3 NBs; location where S4 and S5 NBs will appear indicated by filled and open circles, respectively. Right: All NBs have delaminated. Midline is represented by hatched line. NBs are individually identified by numbers and gene expression pattern (coloring).