No. I.] CONTRIBUTION TO INSECT EMBRYOLOGY. 23 



Soon after the union of the edges of the outer and inner 

 indusial layers a chitinious cuticle is secreted by the outer 

 surface of the latter. This cuticle is thicker and seems to be 

 of a deeper hue than the cuticle secreted by the serosa. It 



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Fig. III. 



Two stages in the spreading of the indusium. A, lateral view of egg just after 

 the arrival of the embryo on the dorsal yolk ; B, lateral view of the egg with the 

 indusium nearly reaching the poles ; C, same egg seen from the dorsal surface. 



definitely excludes the outer indusium from any further share 

 in the development of the embryo. Even in Stage E, this cell- 

 layer was reduced to an exceedingly thin membrane. (PI. 

 Ill, Fig. 22, am.^) It seems to fuse with the serosa and to 

 retain a connection with the inner indusium only at the ex- 



