182 GEORGE E. NICHOLLS 
and fixation, therefore, had necessarily been slow. I have sug- 
gested (12 a, p. 27) that unusually strenuous exertions made by 
the animals in their unavailing efforts to avoid capture may be 
the cause of the somewhat frequent instances of broken fiber 
noted in these cyclostomes.®> Careless handling of the specimens 
might be equally responsible for the snapping of the fiber. It 
is possible, therefore, that the apparent absence of the fiber 
from the spinal cord of specimens which have been some time 
dead before fixation may not be due (as I have supposed) simply 
to the degeneration of the fiber having already occurred, but 
may be owing rather to its having been broken and retracted 
entirely beyond the limits of the piece or pieces of tissue 
examined. 
In two rays which, although not the subjects of experiments, 
manifested a well marked reaction a spirally coiled condition was 
discovered in the broken fiber. One (Raia XIX) is known cer- 
tainly to have been taken some 24 hours before the material was 
preserved and it is probable that a similar interval had elapsed 
between the capture and preservation of the material in the 
case of the second (XXXIX) also. The former bore signs of 
recent damage in the tail region evidently caused by the trawl 
but the other appeared externally to be undamaged. If, there- 
fore, the fiber had been broken at the time of capture, in conse- 
quence of the violence of the animal’s struggles to escape, the 
fiber might be expected to have become straightened out or to 
be in the process of unwinding. In one (XX XIX) the free end 
of the fiber is loosely curled (fig. 20) and in the other (XIX) a 
tangle remains as evidence of a sharp recoil, but the spiral wind- 
ing is found only in the vicinity of the tangle (fig. 25) and has, 
elsewhere, disappeared. 
That the fiber was liable, in its recoil, to form intricately 
tangled knots or ‘snarls’ was first noticed by Sargent (’04, fig. 
8). His figure does not suggest the spiral winding which I be- 
lieve to be associated with the recent contraction of the fiber 
and which is seen in the photomicrograph which I published 
in 1912 (’12, fig. 3). 
5 The breaking of the fiber, prior to the experiment, in nos. 3 and 49 is prob- 
ably to be attributed to this cause. 
