EMBRYONIC ENVELOPES, DORSAL ORGANS, BLASTOKINESIS 61 



and thereupon takes on the usual functions of the serosa during the 

 revolution of the embryo. .The eggs of these grasshoppers thus have the 

 following envelopes, passing from without inward in a median transverse 

 section of the egg: chorion, vitelline membrane, cuticula secreted by 

 the serosa, serosa, outer indusium, cuticula secreted by the inner indusium, 

 a layer of granular substance, inner indusium, and amnion, the last one 

 covering only the embryo (Fig. 37). A complete indusium has been 



Fig. 37. — Xiphidium erisiferum. The indusium. (am) Amnion, (emb) Embryo. 

 iind) Indusium: (ci) cuticula of inner indusium, (i) inner, (o) outer, {ser) Serosa. Cho- 

 rion, vitelline membrane, and cuticula secreted by serosa, omitted from figures. {From 

 Wheeler.) 



described bj^ Muir and Kershaw (1912) for the homopteran Siphanta 

 acuta. Hagan (1917) found an indusium-like mass of cells in the mantid. 

 It remains attached until rotation, when it becomes free, later to be 

 ingested during the formation of the dorsal body wall. The possible 

 homology of the primary dorsal organ with the indusium of Xiphidium 

 has been pointed out by Willey (1898), but this seems unhkely. The 

 structure suggests an abortive twin embryo in its manner of development, 

 the outer layer comparable to the amnion, the inner to the embryo. The 

 grumorium described by Miller (1939) seems to be an analogous develop- 

 ment. Further investigations are necessary before it is safe to pronounce 

 judgment as to the homologies of these anomalous structures. 



