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Wheeler, however, compares with the “dorsal organ” the peculiar extra embryonic membrane or indusium which he has observed between serosa and amnion in the embryo of the grasshopper Xiphidium.

Indusium: the case made by an insect larva: a membranous layer of the embryo of Locustidae below the serosa.

This depends upon whether the inflammation of the serosa quickly spreads or remains local.

In some midges and in caddis-flies the serosa becomes ruptured and absorbed, while the germ band, still clothed with the amnion, grows around the yolk.

S, serosa; A, amnion; E, ectoderm; N, rudiment of nerve-cord; M, mesodermal pouches.