THE LAMPREY EYE 



559 



The iris merges directly into the chorioid opposite the ora terminalis 

 of the retina, without the intermediation of a ciUary body — since there 

 are no ciUary muscles, ciliary processes, or zonule fibers, for which attach- 

 ments need be supplied. The perfectly spherical lens is held against the 



a ^XaragnJ 



Fig. 162 — Retina and optic nerve of Lampetra fluviatilis. 



a, appearance in ordinary histological preparation, x 500. 



a- amacrine cells; b- bipolar nucleus; c- cone; g- ganglion cells; h, h- horizontal cells; 

 m- Miiller fiber; n- nerve-fiber layer; o- outer nuclear layer; p- pigment epithelium; r- rods; 



b, neurological schema, based upon Bielschowsky preparations, x 250. After Tretjakoff. 



a, a- amacrine cells (six types); b,b- bipolar cells (five types); c- cone; e- external limit- 

 ing membrane; g- ganglion cell; h- horizontal cells; i- internal limiting membrane; m- 

 Miiller fiber; n- nerve-fiber layer (= ganglion-cell axons); r- rod. 



c, cross-seaion of optic nerve and its sheaths. From Franz, after Diicker. 



d- dural sheath; pa- pia-arachnoid sheath; n- nerve-fiber mass; e- ependymal cell-bodies; 

 oa- ophthalmic artery. 



