12 



EMBRYOLOGY OF INSECTS AND MYRIAPODS 



On the dorsal side a small group of cells invaginates slightly and later 

 is absorbed in the yolk. This small group of cells constitutes the primary 

 dorsal organ (do). Similar structures, apparently homologous, have been 



ser 





do4r. 



Fig. 10. — Germ-band formation. 

 A, sagittal section. B, cross sec- 

 tion, (do) Dorsal organ, {gb) Germ 

 band, {ser) Future serosa, {yc} Yolk 

 cells. 



ser 



Fig. 11. — Formation of embryonic 

 envelopes. A, sagittal section. B, cross 

 section, (am) Amnion, (am.cav) Amni- 

 otic cavity, (gb) Germ band, (gc) Germ 

 cells. (W) Head lobe, (ser) Serosa. 

 iyc) Yolk cell. 



described for the embryos of Endromis (Lepidoptera), the honeybee, and 

 other insects. 



The Embryonic Envelopes (Amnion and Serosa). — After the germ 

 band is well defined and with well-developed head lobes (hi), the caudal 



