tpi.7- 



FiG. 25. — Astacns flnv'mtilis. — The central nervous system seen from 

 above (nat. size), a, vent ; «w, antennary nerve ; a! 11, antennulary 

 nerve ; e, circum oesophageal commissures ; gn. 1, supracesophageal 

 ganglion ; gn, 2, infraoesophageal ganglion ; gn. 6, fifth thoracic 

 ganglion ; gn. 7, last thoracic ganglion ; gn. 13, last abdominal gang- 

 lion ; ces, oesophagus in cross section; on, optic nerve; sa, sternal 

 artery in cross section ; sgn, stomatogastric nerve. 



