THE FUNCTION OF REISSNER’S FIBER Ta 
occurred an extensive withdrawal of the fiber, forward, from the 
region of the experimental lesion. 
In a couple of instances (47, 64) this relation is less evident, 
there having been a somewhat pronounced reaction although the 
fiber had not been very greatly retracted. Both of these speci- 
mens were the subjects of experiments of quite short duration 
(11 hours and 10 minutes respectively) and it is probable that 
the fiber would have continued to retract had the experiments 
been allowed to proceed for a longer period. 
Reissner’s fiber, in three specimens (5, 7, 24), all of which were 
the subjects of experiments of prolonged duration, is found to 
extend backwards nearly or quite to the region of the experi- 
mental incision. 
A secondary sinus terminalis is seen in the process of forma- 
tion in the last of these and in this case Reissner’s fiber has 
become of almost normal diameter but lies freely with a some- 
what fibrillated ending in this new terminal enlargement of the 
central canal. 
The sections through the tails of two other specimens were cut 
transversely and the condition of the end of the fiber can not be 
certainly determined. In one (7) the fiber has a diameter but 
slightly greater than the normal, while in the second (5) it is 
quite distinctly swollen. 
Another specimen (6) is apparently a normal case in which 
there has been a considerable retraction. ‘The terminal piece 
sectioned shows that the fiber had withdrawn wholly from that 
region. The penultimate piece, however, contains the free end 
of the fiber lying slackly and of quite notable slenderness. I 
suspect that this may be an early phase of regeneration in which 
a delicate new growth of fiber is stretching backward, the usual 
simple straightening out of the original thread having, for some 
reason, been prevented. 
4. Regeneration is seen ina well advanced condition in but 
a single specimen (2), a dogfish, of which the condition of the 
end of Reissner’s fiber is seen in figure 31. In front of the in- 
cision, a secondary sinus terminalis has arisen, the pia mater 
having grown around the end of the filum terminale where it 
