gm.e 



ffn.7- 



fftva 



tyn /3 



Fig. 25. —Astacus fluviatilis. — The central nervous system seen from 

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

 nerve ; c, circumcesophageal commissures ; gn. 1, supraoesophageal 

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

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

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

 artery in cross section ; sgn, stomatogastric nerve. 



