ORTHOPTEROIDEA (PANORTHOPTERA) 243 



single row, although in the rest of the mass they exhibit no regiilar arrange- 

 ment. This mass is the rudiment of the optic ganglion and eye plate. 

 Several hours later the inner mass, or optic ganglion, begins to separate 

 from the outer layer, or eye plate, the separation being completed in 

 the 80-hour stage. Meanwhile the optic lobe becomes connected with the 

 middle protocerebral lobe which ultimately forms the internal medullary 

 mass of the optic lobe and the optic nerve. During blastokinesis the 

 optic lobe acquires a secondary connection with the eye plate. The 

 nuclei of the optic ganglion near its dorsal edge elongate and send out 

 nerve fibers which go to the retinulae and form the postretinal fibers. 

 The middle, or second, lobe, as noted above, forms the internal medullary 

 mass of the optic ganglion. The median, or third, lobes form the future 

 protocerebral lobes of the brain between which, and arising from which, 

 runs the supra-esophageal commissure. The deuto- and tritocerebrum 

 in mode of origin and futher development are exactly comparable to the 

 ganglion of the ventral chain. Originally they are postoral in position 

 but subsequently shift forward in relation to the mouth so that the deuto- 

 cerebrum is distinctly preoral, whereas the tritocerebrum lies beneath 

 and behind the mouth, its lobes connected by a commissure. The 

 deutocerebral lobes, which at first lie close together, gradually move 

 apart, migrate forward, and lose all evidence of their original connection. 

 The deutocerebrum, from which the antennary nerves arise, has no trans- 

 verse commissure. 



The stomatogastric nervous system arises in the 98-hour embryo 

 as an unpaired group of cells on the dorsal ectodermal wall of the stomo- 

 daeum. The mesodermal coat which surrounds the stomodaeum is 

 wanting in these regions. Afterward, when the masses are well differ- 

 entiated into ganglia and separate from the stomodaeal ectoderm, the 

 mesoderm closes beneath them to form an unbroken ring around the 

 stomodaeum. There are formed a frontal ganglion, an unpaired occipital 

 and paired pharyngeal ganglion arising from a common rudiment, and a 

 third rudiment from which the paired ventricular ganglia arise. These 

 rudiments soon are connected by the recurrent nerve. When the inner 

 walls (ant.co) of the antennary coelom form the cephalic aorta, the 

 pharyngeal ganglia (g.ph) become enclosed in them (Fig. 163). 



The fore-gut develops in the 52-hour stage as an invagination near 

 the cephahc end of the embryo (Figs. 166^,5). At the time of its first 

 appearance its blind end is free from cells of the inner layer but shows an 

 outgrowth of cells that eventually form the mid-gut epithelium. Later 

 the blind end secondarily acquires a covering of inner-layer cells which 

 form the stomodaeal musculature. In the 120-hour stage the blind 

 end broadens out and becomes thin, rupturing when the mid-gut epi- 

 thelium is completed. The hind-gut develops as a proctodaeal invagina- 



