105 



not the case, it passes directly to the base of each rod, 

 where it terminates. Both Patten (35) and Rawitz (36) 

 have followed this structure through the rod cells. Eawitz 

 stated in addition that there was a fine canal running 

 through the middle of the rod cell, in which lay the fibre. 

 Schreiner (37), after making a careful series of pre- 

 parations, came to the conclusion that there was no axial 

 fibre in the rod cell, and that the appearance of one was 

 due to the contours of adjacent cells, or an optical eft'ect 

 formed owing to the rod cells being slightly angular in 

 transverse section and not pei*fectly cylindrical. Hesse 

 (32) acknowledges that it is often extremely difficult to 

 find the fibre in the rod cells, even when it is perfectly 

 obvious in the rods, but confirms Patten, and states that 

 in Pectcn aratus the fibre is easily followed in the rod cells. 

 The eye of Pccten, nuixiimis is not suited for this 

 histological work, but transverse sections made through 

 the retina (figs. 32 and 33), and cutting both rods and rod 

 cells, show how distinctly the fibre is to be seen in the 

 former whereas it is absent in the latter, and here both 

 rods and rod cells have been subjected to exactly the same 

 conditions of fixation and staining. In the Grold Chloride 

 preparations, however, the fibre was seen in some rod 

 cells to extend very slightly above the base, and not to 

 end abruptly but rather to thin out. Apathy's (27) and 

 Bethe's (28) work on the nervous system has thrown much 

 light on the structure, and if we regard the nerve cell as 

 simply a cable, the conducting wires of which are the 

 neural fibrillae and the perifibrillar substance the pro- 

 tective and insulating material, we can apply this to the 

 rod cells. The axial fibre in the rods is a nerve fibril 

 lying in its nerve cell. It is so obvious because it is in 

 all probability the product of the fusion or very close 

 apposition of several primitive fibrillae. 



