|
Figure 2
Development
of the cricket Acheta domesticus, an intermediate germ band insect.
(A) Major features of development. (1) The ventral germ band becomes immersed
inside the yolk and migrates posteriorly. After establishing segmentation,
the embryo revolves around the posterior end of the egg and assumes its
final position. (2-4) The head emerges from the yolk and moves anteriorly.
The embryo begins to progressively cover the yolk sac as tissues differentiate.
(5, 6) The embryo closes its dorsal flanks. The leading edge contains
the mesodermal cardioblasts. (7) Frontal view of the cricket embryo during
the completion of organogenesis. (B) Schematic diagram of the development
of the amniotic cavity in intermediate germ band insects. (1) Lateral
folds starting at the edges of the germ band grow over the germ band.
(2) The lateral folds meet ventrally beneath the germ band. (3) The membranes
fuse, causing the separation of the amnion and serosa, thereby surrounding
the embryo with yolk. (After Schwalm, 1997). |
