272 



EMBRYOLOGY OF INSECTS AND MYRIAPODS 



dorsoventral flattened sack, one wall of which is the embryo, the other the 

 amnion. At first the amnion and the embryo show a similar cell structure 



except at the posterior end at the point 

 of invagination. There the amniotic 

 cavity runs out into two furrows (Fig. 

 202), the inner wall of the invagination 

 representing the prolongation of the 

 amnion, the outer wall the anlage of 

 the germ band. The continuation of the 

 germ band anteriorly is represented by 

 the two ends of the lateral plates, or head 

 lobes, which are still distinctly separated 

 (Fig. 204, hi). When the tail of the 

 invaginating embryo reaches the cephalic 

 end of the egg, it bends and grows caudad 

 until head and tail nearly meet (Fig. 

 203 A) . At the point of invagination two 

 amniotic folds appear (Fig. 203 A, amf) 

 which fuse, with the result that the 

 embryo lies completely separated from the serosa (Fig. 2035). Nearly 

 the same stage in development of Oncopeltus is represented by Fig. 204, a 



hi 



Fig. 202. — Pyrrhocoris. Ventral 

 aspect, {hi) Head lobe. 



proct 



amf 



B 



Fig. 203. — Pyrrhocoris. Sagittal sections. Diagrammatic. A, elongation of embryo. 

 B, shortening of embryo, {am) Amnion, {am. cav) Amniotic cavity, {amf) Amniotic 

 folds, {il) Inner layer, {proct) Proctodaeum. {ser) Serosa, {stom) Stomodaeum. 



sagittal section of an embryo before it has attained its greatest length and 

 while the head lobes (hi) are still on the surface. 



