ORTHOPTEROIDEA (PANORTHOPTERA) 241 



side of the heart. They arise from the somatic mesoderm abutting on the 

 ventrolateral aspect of the heart. The blood cells arise mainly from the 

 median mesoderm but partly also at the junction of the somatic and 

 splanchnic mesoderm or even from the splanchnic mesoderm in the pre- 

 blastokinetic stages. 



The fat body is derived from the larger part of the median and lateral 

 walls of the dorsal section of the coelomic sacs in the thorax and abdomen 



yc y 



Fig. 164. — Locusta. Cross section of heart and upper margin of mid-gut in region of 

 mesothorax. {bl) Blood cell. (c6) Connecting sinus between heart {h) and circumintestinal 

 blood sinus {ih). {cbl) Cardioblast. {ms) Mesentery of circumintestinal blood sinus. 

 {aplm) Splanchnic mesoderm, (y) Yolk, {yc) Yolk cells. 



and also from the lateral walls of the dorsoanal pouch of the antennary 

 coelomic sac. 



The tracheal system is first in evidence in the 112-hour stage as 10 

 pairs of ectodermal invaginations whose mouths form the spiracles 

 (cf. Fig. 159, st). The mesothoracic and metathoracic spiracles subse- 

 quently migrate forward so that the former come to lie on the membrane 

 between the prothorax and mesothorax, whereas the latter come to lie 

 on the posterior margin of the mesothoracic pleuron. At the blind end 

 of each spiracular invagination two diverticula develop: a horizontal, 

 short mediodorsal one and a longer laterodorsal backward-directed one. 

 Later another very short mediohorizontal diverticulum is formed from 

 the spiracular invagination. 



At about 64 hours the neuroblasts first become differentiated as a 

 row of four, rarely five, large cells with massive rounded nuclei, lying 



