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Fig. 25. — Asia ens fluviatilis.—Tl'hQ central nervous system seen from 

 above (nat. size), a, vent ; an, antennary nerve ; a'n, antennulary 

 nerve; c, circumoesophageal commissures ; yn. 1, supracesophageal 

 ganglion; gn. 2, infraoesoijhageal ganglion; ;/«. (5, fifth thoiacic 

 ganglion ; ^». 7, last thoracic ganglion ; (jii. 13, last abdominal gang- 

 lion ; wx, CESophagus in cross section ; un, optic nerve ; ««, sternal 

 artery in cross section ; mjn, stomatogastric nerve. 



