336 



EMBRYOLOGY OF INSECTS AND MYRIAPODS 



mesoderm follows it by a rapid growth along its lateral margins. When 

 the lateral margins come in contact with the yolk, they are reflected 

 backward and inward toward the median line, thus forming, on either 



Fig. 291. — Neophylax. Cross section of first abdominal segment, {ect) Ectoderm. 

 (n) Connective of nerve cord. {som. m) Somatic mesoderm, {splm) Splanchnic meso- 

 derm, (yc) Yolk cell migrating into the body cavity. 



Fig. 292. — Neophylax. Sagittal section of embryo, (an) Anus, (malp) Malpighian 

 tubules, (mes) Mesoderm, (spg) Spinning glands, (yc) Yolk cells. 



side of the body, a mesodermic layer, bounding the yolk on the ventral 

 side. By continued growth the margins finally meet each other (Fig. 

 291). The inner (splanchnic) layer of mesoderm extends over and 

 encloses the yolk to form the muscle layer of the mid-gut. This occurs 

 before the yolk (entoderm) cells have formed the epithelial lining. The 



