232 EMBRYOLOGY OF INSECTS AND MYRIAPODS 



given off from the dorsal wall (Fig. 153, suboesb) increase in size and meet 

 medially to form a cluster of cells that give rise to the subesophageal 

 body. The other cells of the coelomic sacs form muscles. 



The first maxillary coelomic sacs have small rounded cavities (Figs. 

 152, 154), which do not develop a dorsal pouch but correspond to the ven- 

 tral portion of other coelomic cavities. Their walls eventually develop 

 into muscles of the first maxillae. 



The labial coelomic cavities (Fig. 152) first appear at 56 hours. They 

 grow rapidly so that in the 70-hour stage they already show a long dorso- 

 rostral and a short dorsoanal pouch. The ventral pouch fills the hollow 



ecf- 



Fig. 155.^ — Locusta. Cross section of middle of second thoracic segment of 75-hour 

 embryo, (am) Amnion, (bl) Blood cell, {coel) (1) Dorsorostal, (2) dorsoanal, (3) ventral 

 pouch of coelomic sacs, (dc) Provisional dorsal closure, (ect) Ectoderm, (p) Second leg. 



of the second maxillary appendage and forms the labial musculature; 

 the dorsorostral and anal portions contribute to the formation of the 

 splanchnic mesoderm, the lateral myoblast plate, and the fat body. This 

 is the largest of the gnathal coelomic sacs. The small mandibular and 

 first maxillarj^ sacs correspond largely to the ventral portion of the labial 

 coelom. 



The coelomic sacs of the thoracic segments (Figs. 147, 155, 156) 

 develop in a similar manner appearing first in the hollow of their append- 

 ages and lying obliquely to the long axis of the embryo. Their median, 

 dorsoanterior ends are pointed, whereas the lateral, ventroposterior ends 

 are rounded. In the 75-hour stage the coelomic sacs show three distinct 

 pouches: the dorsorostral, the dorsoanal, and the ventral. The rostro- 

 lateral coelomic walls extend medially as a thin, single-layered band over 

 the ectoderm, each fusing with its fellow of the opposite side, forming 

 in this way the blood-cell lamella (median mesoderm) (Fig. 147). A little 

 later (80-hour stage) the segmental mesoderm (Fig. 156) also extends 



