50 



EMBRYOLOGY OF INSECTS AND MYRIAPODS 



as in the Lepidoptera and in some Odonata. In the case of the latter the 

 germ band, instead of sinking beneath the surface to become immersed, 

 invaginates into the yolk. This is the invaginated type of immersed 



amf- 



am.cav 



Fig. 31. — Development and fate of the embryonic envelopes. A, gastrulation. B, 

 formation of amniotic fold. C, completion of serosa (ser). D, fusion of amnion and serosa 

 (am. ser). E, rupture of amnion and serosa. F, shrinkage of envelopes, (am) Amjiion. 

 (am. cav) Amniotic cavity, (amf) Amniotic fold, (ect) Ectoderm, {gastr) Gastrula 

 furrow. (&0O Ganglion. (iJ) Inner layer, (ip) Lateral ectodermal plate, (mgre) Mid-gut 

 epithelium, (ser) Serosa, (y) Yolk. 



germ band. The embryos of many insects remain at the surface during 

 development, in which case we have the superficial type. Certain forms 

 are intermediate in type, as with some Coleoptera in which the anterior 

 part of the embryo remains superficial but the caudal end is invaginated 



