334 



EMBRYOLOGY OF INSECTS AND MYRIAPODS 



In the formation of the primary epitheUum (blastoderm) no yolk 

 cells remain behind in the yolk. Later, during the formation of the 

 embryonic envelopes, amoeboid cells with large nuclei can be seen in the 

 yolk which have migrated back from the blastoderm and have been 

 gradually distributed through all parts of the yolk. These are the yolk, 



:■■■■■ O rPt'-: 



. .y'- . . •••■; a. J -J ^■'.:iA.,Av' ..-s 



. \ •^x^i@:»%v>,..^••■^4.A...A^•-i-'XS-^ 



•v.. 1>*'S./ .■■'■ 



\ft-^f*' 



gastr 



Fig. 287. — Neophylax. Cross section of head region, {am) Amnion, (c/i) Chorion. 

 (gastr) Gastrula furrow, {ser) Serosa. 



or entoderm cells {yc), which arise from any point in the blastoderm by 

 delamination. This process may continue even after a part of the blasto- 

 derm has been converted into the ventral plate. 



The procephalic lobes increase in thickness, and the embryo lengthens 

 until head and tail almost come in contact with each other (Fig. 290, 

 ceph). After the appearance of the proctodaeum the posterior end of the 



•i '•■"•» \) Ox.-'-'-D / 



VkSX o C X>- ^-K ^ / 



/'. 



am 

 ser 



Fig. 288. — Neophylax. Cross section of head region, {am) Amnion, {ch) Chorion. 

 {m,es) Mesoderm, {ser) Serosa. 



body becomes bent forward on itself, marking the first step toward 

 revolution of the embryo. At the stage when head and tail are in close 

 proximity with each other, the rudiments of antennae, mouth parts, and 

 legs appear. 



The neural groove begins at the anterior end of the body and extends 

 to the place where the proctodaeal invagination is to appear. Certain 



