THE EYE OP PECTEN. 87 



became connected with the axial fibres of neighbouring cells 

 (see Patteu^s fig. 140, Taf. 32). Furthermore, he describes 

 how towards the lower ends of the rod-cells the axial nerve- 

 fibre begins to give off radiating fibrillte, which are so 

 numerous in the rods as to constitute the greater part of 

 their substance. Hensen was the first to see the axial fibre 

 in the rod. Patten figured it as being equally distinct and 

 of the same diameter in rod-cell and rod. Rawitz found, 

 however, that there was a fine canal running through the 

 former in which lay the fibre, which, he adds, is the continua- 

 tion of a nerve-fibre from the proximal branch of the optic 

 nerve. This central canal and fibre was supposed to be 

 present in the rod but terminated without the complicated 

 connections of Patten. Carriere, in his second paper (an 

 answer to Patten's criticisms of his first) (26), could not bring 

 the existence of a nerve-fibre inside a cell into line with 

 histological teaching, and hence said that what was present 

 was simply a differentiation of the cell-substance. Schreiuer 

 came to the conclusion that a detailed examination was 

 necessary owing to the diverging opinions of previous authors, 

 and found after making sections and teased preparations 

 that there was no axial fibre at all in the rod-cells, and what 

 had been seen there was only one of the contours of a rod- 

 cell produced by pressure causing these normally cylindrical 

 cells to be angular. He found it very distinctly stained, 

 however, in the rods, and it ran straight to the end where it 

 terminated in a point. He adds that it differs somewhat 

 in staining qualities from nervous tissue and is too thick for 

 a nerve fibre (p. 72). 



Hesse found after all this research that it was necessary to 

 go back to the earlier views, for he made out the axial fibril 

 running through both rod-cell and rod. 



He states, however, that it is far more easily seen in the 

 rods, and even there it varies in the same preparation. 



It is less distinct in the rod-cells because thinner (except 

 in P. aratus), and in some cases Hesse saw more than one 

 present. This bring us to Hyde's views (39) regarding rod- 



