ORTHOPTEROIDEA {PANORTHOPTERA) 



225 



The protoplasmic reticulum is not distinct in early stages, but with 

 the diminishing yolk in the older stages it becomes evident. At about the 

 sixtieth hour the j^olk, which so far presents an amorphous appearance, 



Fig. 141. — Locusta. 



; section of 45-hour germ band, (ect) 

 layer, (vg) Second ventral groove. 



Ectoderm, {il) Inner 



begins to show polyhedral differentiation in the immediate neighborhood 

 of the embryo. By the seventy-fifth hour the entire mass is divided into 

 polyhedral masses, which 24 to 36 hours later completely disappear. 



am.cav. 



Fig. 142. — Locusta. Cross section of hind region of protocerebrum of 42-hour germ 

 band, (am) Amnion, (am. cav) Amniotic cavity, (ect) Ectoderm, (il) Inner layer. 

 (ser) Serosa, (y) Yolk, (yc) Yolk cell. 



Not all the cleavage cells reach the egg periphery to form the primary 

 epithelium (blastoderm), some remaining in the yolk to form the vitello- 

 or primar}^ yolk cells, stellate cells with large round nuclei. 



arn.cav eci il am ser ch mi 



Fig. 143. — Locusta. Cross section of posterior end of 45%-hour embryo, (am) 

 Amnion, (am. cav) Amniotic cavity, (ch) Chorion, (ect) Ectoderm, (il) Inner layer. 

 (mi) Micropylar canal, (ser) Serosa. 



Secondary yolk cells may arise by inward migration or by division of the 

 primary epithelial cells, the inner product forming the secondary yolk 



