THE EYE OF PECTEN. 9] 



ascribed to it by Hesse. Often the more delicate rod is 

 broken up in maceration and the axial fibre is then left 

 sticking" out from the protoplasmic remains of the cell (PI. 7, 

 fig. U,Ax.f.). 



After seeing these preparations one is rather inclined to 

 believe that this is also a supporting structure. 



In sections, however, the appearances are more favourable 

 to the nervous view. The separation of the components of 

 the axial fibre is similar to that often taking place in neuro- 

 fibrillse, and the fibre occurs in a sense-cell and stains always 

 like the nerve-fibres in the same preparation. In the rods 

 the axial fibre differs somewhat in appearance from a typical 

 neurofibril in thickness and distinctness. These structures 

 considered as the conducting elements of the nervous system 

 were unknown to the earlier writers on the Pecten eye. 



There are two views, then, that may be taken of the function 

 of these fibrilhe. We may regard the axial fibril in the rod 

 as a true neurofibril, a "primitive fibril" formed by the 

 apposition of several elementary fibrillge which pass through 

 the rod-cell, the apposition occurring normally or through 

 fixation. These neurofibrillse have, then, the function assigned 

 to them by Apathy and Bethe — the conduction of nerve 

 impulses. On the other hand we may consider the whole to 

 have only the function of a system of supporting fibres. The 

 latter view would resemble that put forward by Nansen and 

 accepted by several investigators, who consider the neuro- 

 fibrillae to be the supporting, and not the conducting elements 

 of the nerve-cells. It is also conceivable, of course, that the 

 structures are not homologous with the neurofibrillse of nerve- 

 cells at all. 'I'here is at present, to vay mind, much confusion 

 existing in reference to fibrous structures in nerve-cells, 

 especially since Holmgren has shown (37) that processes of 

 the neuroglia actually penetrate into ganglion cells and act 

 as supporting fibres. 



An axial fibril of the same type as that occurring in the 

 Pecten eye is a feature of the rod-cells of many other inver- 

 tebrate eyes. For example, in the Lamellibranchiata it is 



