Fig. 6.

Schematic comparison of extraembryonic zen expression between holometabolous insects. Successive developmental stages of Tribolium (A), Megaselia (B), and Drosophila (C) are shown with zen-expressing extraembryonic tissue depicted in red. Prospective extraembryonic tissue that does not express zen is depicted in blue, and embryonic tissue is in green. Note spatial differences of zen expression between species and the down-regulation of zen in Drosophila at about the same developmental stage that the preserosa of Megaselia begins to expand beyond the distal edge of the amnion. Anterior is left, and dorsal is up.