NOTE ON THE EYES OF CAKUrUM MUTIOUM Ueev^. 281 



rritudiiial section, we lind that the cells of the lens are arrauf^ed ior the 

 most part in two lonuitiKlinal eoJumu.s. The cells are nucleated, 

 havins' nuclei near the external surface of the lens. 



The n'luia (üg. 2, rcl.) is in contact with, and directly below, the 

 lens. It is very sim])le in structure, consisting of colourless, columnar 

 cells arranged in one layer. These cells have rods (tig. 2. ro.) 

 which are not clearly fjund in the eye of Cdrdiimi cdule (Patten,* 

 J:îutschli **). The rods are directed away ironi the retino})horae and are 

 separated from them by a jtseudoniembrane. They seem to be hollow, as 

 they appear as rings in cross section of some well ])reserved specimens. 

 They are longest at the optic axis and gradually diminish in length as 

 the distance from the optic axis increases. They are stained homogene- 

 ously and rather deeply. As regards the retinophorse, the nuclei are 

 deeply stained, while the protoplasm is very faintly stained. I could 

 not find the ganglionic-cell layer, although it is stated to be ])resent in 

 the eyes oï Pect en and Canlimn edulc (Patten, Biitschli). 



lîelow the retina and continuous with it at the circinnference, 

 there is a layer of fiat cells (tig. 2. c//.). These cells, are small and thin 

 at the juncture with the retina, so that it is difticult to tind out tliis 

 connection in well develo])ed eyes. 1 shall name tliis layer as the 

 choroid, as it seems to ht. liomolog<jus in position to tiie pigment epithe- 

 lium of the choroid of the \ertebrates. If the ta])etum (argentea of 

 Patten) of Peclcn and Curdimii e.dide is cellulai' in orign, as it is stated 

 to l)e, tVie cjioroid oï Cardimii )tnificinii is j)robably homologous with it. 



Below the chorijid there is a membranous layei". It is the iapctuvi 

 (fig. 2. t.). It consists of many thin, shining layers, stained deeply 

 and homogeneously by colouring solutions. 1 cannot tind any sign of 



* Patten— /oc. cit. 



** Biitschli — Notiz zur Morphologie des .Vllgo^^ der Muscholu. (Zoologisches Jahresljoricht 

 für 1886). 



