i6 



WHEELER. 



[Vol. VIII. 



I shall retain the old name; the corresponding envelope of the 

 indusium and the body of the organ will be designated as the 

 outer and inner indusium respectively. 



In by far the greater number of cases the process of 



\.»2^— 



,...„(»*. 



Fig. II. 

 Diagrams illustrating the movements and envelopes of the Xiphidhtm embryo. 

 A, after the closure of the amnioserosal folds ; B, during the embryo's passage to 

 the dorsal surface ; C, just after the straightening of the embryo on the dorsal 

 surface, ind., indusium — afterwards forming /wo'S the inner, and ind^, the outer 

 indusium ; ch., chorion ; sr., serosa ; am., amnion ; gb., germ-band ; v., yolk ; bl. c, 

 Blastodermhaut. 



envelope formation over the indusium is much obscured by 

 rapid slurring. In fact the whole process has frequently the 

 appearance of being due rather to a shifting and migration 

 of cells than to the formation of true folds. The cells of the 

 serosa seem to creep over the disk while the cells forming the 



