ORTHOPTEROIDEA {PANORTHOPTERA) 



215 



The muscles of the mid-gut are formed from the splanchnic (visceral) 

 layer of the coelomic sacs. Blood cells arise from the median part of the 

 mesodermal layer which originally connected the right and left halves. 

 The fat body arises from a part of the latero ventral wall of the sacs, at 



first only an inconspicuous mass but later 

 filling a considerable space in the defini- 

 tive body cavity. As has been described 

 for other Orthoptera, the pericardial 

 septum develops from the dorsad-growing 

 part of the somatic mesoderm, the heart 

 from the crescent-shaped cardioblasts 

 (mesoderm derivatives at the dorsal 

 junction of somatic and splanchnic 

 layers). A delicate ental membrane, 

 similar to that described for Locusta, 

 Pteronarcys, and some other insects but 

 heretofore not recorded for Blattella, has 

 been observed by Dr. L. C. Pettit. 



Fig. 131. Fig. 132. 



Fig. 131. — Blattella. Mid-sagittal section of amniotic fold at caudal end. {am) Amnion. 



(ecO Ectoderm. (iO Inner layer, (ser) Serosa. 

 Fig. 132. — Blattella. Caudal migration of nine-day embryo. 



The germ cells in the roach are segregated from the median caudal 

 groove during or shortly after segregation of the mesoderm but before 

 mesoderm segmentation and before the formation of the coelomic sacs. 

 Later they migrate forward, are carried dorsad, and come to lie in two 

 strings extending from the second to the seventh segments after having 

 passed through the splanchnic layer into the genital ridges. Here the 

 paired anlagen of the gonads are formed. 



