ORTHOPTEROIDEA (PANORTHOPTERA) 



21' 



division reach the surface, where they continue to divide much more 

 actively in the posterior half of the egg. A few yolk cells remain in the 

 yolk. Later a small, nearly circular germ disk forms at the posterior end 

 of the egg; the nuclei of the cells of the remaining primary epithelium 

 (blastoderm) are widely separated. 



No gastrula invagination is formed in the embrj^o of this termite. At 

 irregular points in the embryonic area, lateral as well as median, some 

 cells are pushed below the surface, and others are separated toward the 

 inner surface of the ectoderm by tangential divisions of its nuclei at 



am 



anir 



am.cav ^„^.. 



am.cav am 



Fig. 133.— a, 

 Amniotic cavity. 



B, Eutermes. Median sagittal sections, (am) Amnion. (,am. can) 

 {antr) Anterior end of germ band, {ch) Chorion, {mes) Mesoderm. 



{ser) Serosa, {yc) Yolk cells. 



various scattered points; an inner layer, constantly gaining in bulk, is 

 thus formed. The amnion appears as a fold at the caudal end of the 

 embryo, its structure at this stage not differing from that of the embrj^o 

 in contrast to the remaining primary epithelium or serosa (Fig. 133 A, am) 

 which is thin, its nuclei far apart. The amnion is thus merely a special- 

 ized portion of the germ disk, or embryo. As development continues, the 

 amniotic tail fold grows over the embryo, neither head nor lateral fold 

 developing (Fig. 1335, am). The mesodermal collection of cells first lies 

 under the anterior half of the germ disk. The yolk-cell nuclei are of 

 remarkable size and apparently remained undivided from an early stage. 

 The cells of the embryo as well as those of the amnion have become 

 smaller by repeated divisions, whereas those of the serosa are compara- 



