TRICHOPTERA AND LEPIDOPTERA 



345 



set free opposite the point of the stomodaeal invagination (Fig. 301). 

 By the time the embryo is 52 hours old, the anterior cell mass has been 

 forced away anteriorly and laterally from the apex of the invagination, 

 and caudad of it the subesophageal body (Fig. 303B,suhoesh) is devel- 

 oped. In the more generalized Orthoptera this body originates as a 

 paired structure, but in Diacrisia it is vaguely bilobed. 



A B 



Fig. 303. — Diacrisia. Median longitudinal section of 52-hour embryo. A, procto- 

 daeum (proct). B, cephalic end. (am) Amnion, {coel) Coelomic cavity, {stom) Stomo- 

 daeum. (suboesb) Subesophageal body. 



The preoral region is lined with a single layer of cells. The tip of the 

 stomodaeal invagination at 57 hours has become quite thin (Fig. 3045) ; 

 the labrum (Ir) is well developed; and the neuroblasts (neur), char- 

 acterized by their larger size, lie below an irregular layer of mesoderm in 

 the cephahc lobes. At 59 to 60 hours the coelomic sacs, though quite 

 small, have reached their fullest development in head segments four to 





am 



A B 



Fig. 304. — Diacrisia. A, cross section of abdomen of 52-hour embryo. B, cross 

 section of head at 57 hours, {am) Amnion, (coel) Coelomic cavity, (.lim. m) Limiting 

 membrane of the stomodaeum. (Ir) Labrum. {mes) Mesoderm, {neur) Neuroblast. 

 (neurg) Neural groove. 



six (Fig. 305, coel) with a single pair in the preoral region. At this time 

 also the mouth parts have distinctly elongated, though their segmenta- 

 tion is not yet evident (Fig. 3055). 



Meanwhile segmentation of thorax and abdomen, which began after 

 40 hours, has distinctly progressed. At 48 hours (Fig. 302) the meso- 

 derm clearly shows a segmental character. The neural groove is deep 



