THE FUNCTION OF REISSNER’S FIBER 175 
which continues much swollen to the forward end of the piece 
of tissue sectioned. ; 
In a second specimen of the same species showing the charac- 
teristic reaction (Raia clavata, XX XIX), the free end of the 
broken fiber was found near the sinus terminalis swollen and 
loosely spirally coiled (fig. 20). In this case I have no note as to 
the date of the capture. Almost certainly, however, the specimen 
was one of a batch of small rays (of which others were 38, 39, 
40) which had been brought in on the previous day. As in 
the previous specimen, the end of the central nervous system 
appeared quite uninjured (apart from Reissner’s fiber) and in 
this case there were no signs of external injury. 
In two other rays showing the reaction (XXXV and LX XIII) 
there was evidence that the fiber had been broken for, in both, 
the fiber was found lying slackly in the region examined (the 
filum terminale) and in the case of the former it was distinctly 
swollen, but the free end was not found in my sections. 
Another ray (X XXIII) and a dogfish (P), although mani- 
festing the usual reaction, retained a normal condition of the 
fiber in the tail region, of which alone sections were examined. 
It is seen stretching apparently tensely and of normal size and 
it is probable that the fiber must have been broken in a region 
too remote to cause a disturbance of the fiber in the terminal 
filament. 
VII. DISCUSSION 
1. The function and mode of action of the Reissner’s fiber apparatus 
In an earlier paper (712, p. 429) I showed that the breaking of 
the fiber in life generally resulted in the recoil of the severed 
ends, and I concluded that the effect of such a breakage was to 
bring about a temporary loss of control over the pose of the body 
when at rest (and probably also whilst in motion). 
Where the fiber is broken from natural or accidental causes it 
appears that retraction of the broken end almost invariably 
ensues, but in the subjects of the experiments this retraction 
may be, for a while, delayed or even prevented altogether. It 
