THE FUNCTION OF REISSNER’S FIBER 125 
described by Tretjakoff as projecting into the lumen of the 
central canal where each is said to end in a small knobbed proc- 
ess, which Tretjakoff compares to the bellpush of an electric 
bell. He supposes that the stimulation of these cells is effected 
by the pressure of the fiber upon these processes whenever the 
body is flexed. 
That Tretjakoff’s investigations were made upon material 
in which the fiber had been broken and had retracted is suggested 
by his figures. Two only of these depict the central canal. In 
one (fig. 20) the fiber (which is invariably very fine in the Ammo- 
coete) is seen indistinct and vastly swollen. In the other (fig. 
19) the fiber is absent and the lumen of the central canal is 
occupied by nuclear bodies, the remains probably of epithelial 
cells dislodged from the ependymal epithelium by the fiber in 
its withdrawal. Under these circumstances it is not surprising 
that Tretjakoff failed to find the delicate filaments which seem 
to join the fiber at frequent intervals as I have described (12 a) 
and the occurrence of which has been confirmed by Studincka 
(435 py 585) 
The little knobs (Tretjakoff’s bell-pushes) are almost certainly 
the retracted remnants of the fibrillae of those cells which, in 
my view contribute to the formation of the fiber and which, 
torn free by the dislocation of the fiber, have shrunk back upon 
the sensory process of the parent cell. 
B. Earlier attempts to determine the function of Reissner’s fiber by 
experimental methods 
The first reference to experiment in connection with the ques- 
tion of the function of Reissner’s fiber occurs in a preliminary 
paper by Sargent (01). These experiments were subsequently 
described in greater detail in 1904. 
In these experiments an attempt was made to break the fiber 
by a means of incision made through the choroid plexus of the 
fourth ventricle of certain elasmobranchs. Such experiments, 
involving, as they necessarily did, the risk of serious disturbance 
to the central nervous system or even actual injury to the brain 
