GANGLIONIC NERVOUS SYSTEM 



523 



Figs. 692 and 693. — The Right Eye-stalk of the Crayfish, C am b arcs. 



OC, OCj ■ . - 



Fig. 692. — The dissected eye-stalk, with the cutk-ular covering and the sheath 

 enveloping the optic lobes removed. 



F^, fibre tract from supra-oesophageal ganglion to sinus gland ; F^., fibre tract 

 from medulla terminalis to sinus gland ; L, lamina ganglionaris (optic ganglion I) ; 

 ME, medulla externa (optic ganglion II) ; MI, medulla interna (optic ganglion III) ; 

 MT, medulla terminalis (optic ganglion IV) ; OC'i, oculomotor nerve I ; 0C.2, 

 oculomotor nerve II ; SE, supra-oesophageal (cerebral) ganglion ;] SG, sinus gland ; 

 XO, x-organ (J. H. Welsh, J. exp. Zool.). 





__ / 





IV^ 



Fig. 693. — Section through the ej'e-stalk. 



On top is the compound eye with the retinal cells, R, at the proximal end of 

 the ommatidia. The sub-ocular" space, S, is occupied largely by pigment and between 

 it and the retinules is the basement membrane, B. Occupying tlie main body of 

 the stalk are the four optic ganglia, I to IV (lamina ganglionaris, external and 

 internal medulla^, and the medulla terminalis) (Xorman Ashton). 



