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TEXT-BOOK OF ENTOMOLOGY 



of Viallanes. The first pair of primitive ganglia, and which is 

 situated in front of the mouth, is divided into three lobes. 



The first or outermost lobe, according to Wheeler, forms the optic 

 ganglion of the larva and imago, while the second and third lobes 

 (jpc 2 , ^c 3 ) ultimately form the bulk of the bf ain proper, or the pro- 

 tocerebral lobes. The second (primitively postoral) brain-segment 

 or pair of ganglia gives origin to the antennae, while the third brain, 



FIG. 246, A-D. Diagrams of four consecutive stages in the development of the brain and nerve- 

 chain of the einhryo of Xiphidium : I, cephalic, II, thoracic, III, abdominal, region; *t, 

 stomoda-uni or primitive mouth ; </, anus; e, optic plate ; pc(f>ff), 1st protooerebra] lobe, or optic 

 ganglion ; j>c-, />o 3 , !M and 3d protocerebral lobes ; dc, deutoct'rebrum ; tt-, trttocerebrun ; 1-16, the 

 16 postoral ganglia; po.o, postoral commissure ; fp, furcal pit; ac, anterior, pc, posterior, gan- 

 glionic commissure ; ag, anterior, pg, posterior, eg, central, Iff, lateral ganglioineres. After 

 Wheeler. 



or premandibular (intercalary) segment, gives origin to a temporary 

 embryonic pair of appendages found in Anurida and Campodea (the 

 premandibular ganglia), and also to the nerves supplying the labrum. 

 These three pairs of ganglia later on in embryonic life bcmmc 

 preoral, the mouth moving backwards. The three pairs of primitive 

 ganglia, behind, i.e. the mandibular and 1st and 2d maxillary gan- 

 glia, become fused together to form the suboesophageal ganglion, 

 and which in larval and adult life is postoral. 



