427 
1) Two specimens (3, 8) in which a recoil of the fibre in either 
direction from the point of lesion certainly did not occur. 
2) Those in which marked recoil of the fibre has taken place (10) 
and in which uncoiling of the fibre must have followed (4, 5, 7 and F). 
3) One specimen (2) in which regeneration is already well ad- 
vanced. 
i, 
The specimens in the first category were killed very soon after 
the operation and the sections show that in the case of (8) the cut 
ends of the fibre had been prevented from recoiling by the pressing 
together of the walls of the terminal filament. This case was the only 
one in which on recovery from the anesthetic there was a practical 
absence of the usual reaction (vide ante). 
An examination of sagittal sections through the tail of the other 
specimen (3) included here also showed that there had been no re- 
traction of the fibre either forward or backward from the point of the 
experimental incision. On the other hand, it might have given the 
usual reaction had it recovered from the anesthetic, for it is quite 
probable that in many cases the fibre did not spring immediately but 
was lightly held at the point where it was severed and only later 
dragged free when the animal became so active on recovering from 
the effect of the anesthetic. Be that as it may, No. 3 resembles 
No. 8 in that the fibre had not sprung backward as the result of the 
severance of the fibre and that in both the sinus terminalis is preserved 
intact (Pl. II, Figs. 4, 5). No. 3 possesses a further interest in that 
REISSNER’s fibre shows a loose spiral twisting in the terminal sinus 
which clearly can not be the consequence of the experiment and can 
therefore be explained only as still another instance of the occurrence 
of accidental breakage of the fibre during life. In this same specimen, 
also, the remarkable coiling of that part of the fibre in front of the 
incision (Pls. I, II, Figs. 7, 8, 9) can have nothing to do with the experi- 
ment, for the cut (posterior) end of the fibre was held fast, nor can 
it have been simply the result of cutting off this piece of the tail 
before fixation was completed in that region, for the coiled fibre extends 
to the very anterior limit of the piece removed, so that the length of 
fibre which is included must be many times the length of that piece 
of the spinal cord which contains it. The only explanation which I 
can offer for this condition is that the brain may have been removed 
before the whole length of the spinal cord and fibre was hardened, 
and that the retraction noted followed upon the severance of the fibre 
just behind the medulla. 
