OLIGONEPHRIDIA 



211 



edges grow dorsad. It should be remembered that the amnion now in 

 large part forms an envelope around the yolk and that there is greater 

 space for the development of the organs. As 

 development progresses, the lateral edges of 

 the body wall close over on the dorsal side, 

 appendages attain their definitive shape, the 

 cuticula is formed, and red pigment appears 

 in the eyes and on the sides of the abdomen. 

 Going back now to the time of stomodaeal 

 invagination, it will be observed that, as this 

 invagination deepens, it breaks through the 

 underlying inner layer, forcing the extreme 

 anterior end of this layer into the antennal 

 segment (Fig. 210A). The part of the inner 

 layer that lies immediately behind the 

 stomodaeum is not arranged in a single layer 

 of cells, as is the remainder (Fig. 210.4), but 

 forms an irregular mass which later separates 

 from the more posterior portion and grows 

 over the tip of the stomodaeum (Fig. 2105). 

 This compact mass forms the anterior mesenteron rudiment which slowly 

 grows in the form of two posteriorly directed ribbons from which in part 

 the mid-gut epithelium will develop (Fig. 210C). 



Fig 200 — Pyrrhocoris 

 A.ftei blastolviiicsis Retracted 

 serosa {ser) covering the head. 



stem 



sfom 



A Be 



Fig. 210. — Pyrrhocoris. Sagittal sections of anterior end. A, early stage. B, later 

 stage. Median sagittal section. C, parasagittal section of same age as B. (am) Amnion. 

 {il) Inner layer, {mds) Median strand (middle plate), {mge) Mid-gut epithelium, (pa) 

 Paracytes. {stem) Stomodaeum. 



At the posterior end of the germ band the inner layer is distinctly 

 thicker than that at the anterior end. A posterior portion of it, in contact 



