THE FUNCTION OF REISSNER’S FIBER 161 
tail reaction, if that were produced. The ray was killed at 1 p.m. 
next day. Duration of experiment 1 day ? hours. 
The fiber had apparently retracted forward, completely beyond the 
anterior limit of the terminal piece sectioned. 
42. In this experiment, also, the cut (made at 6.05 p.m., August 17) 
accidentally severed the tail, a piece scarcely one-sixteenth of an inch 
in length being removed. The specimen assumed the vertical posi- 
tion, both in swimming and at rest. Induced to settle upon the floor 
of the tank, it remained in a nearly normal attitude, the snout only 
being somewhat raised. It was killed at 4.30 p.m. on August 19. 
Duration of experiment 1 day 225 hours. 
The sections are poor and very oblique near the hinder end. Reiss- 
ner’s fiber cannot certainly be made out near the point where it was 
cut. Further forward it is seen here and there and then appears of 
normal diameter, lies centrally and is apparently tautly stretched. 
Probably no retraction took place, but the cut end was gripped by the 
walls of the filum terminale. 
45. The incision was made at noon, August 18. The ray rested in a 
vertical position but the tail was not deflected from the line of the long 
axis of the body. It maintained this attitude and was killed next day, 
no reaction being noted. Duration of experiment 1 day 35 hours. 
In this specimen, the fiber seems to have been prevented from re- 
tracting forward by the grip of the adpressed walls of the filum ter- 
minale, while behind the point of injury a clot has formed in the cen- 
tral canal and apparently the free end of the severed portion was held 
by this clot. 
46. The incision was made at 12.10 p.m., August 18, and at 2.30 
p.m. the end of the tail was seen to be slightly raised. This reaction 
wore off during the afternoon and the ray seemed perfectly normal 
next day. It was killed at 3 p.m. Duration of the experiment 1 day 
2? hours. 
In this ray, Reissner’s fiber is remarkably delicate. It les a little 
slackly, apparently, but otherwise shows no sign of retraction. For 
some distance it lies embedded in an elongated blood clot. 
47. The incision was made at 3.30 p.m., August 19. On recovery 
from the anaesthetic, the fish settled in a corner of the tank with its 
tail raised several inches and resting against the wall of the tank. 
Later it was gently moved away from the vicinity of the wall and it 
then brought down the tail to the tank floor. It was killed at 4.45 
p.m. Duration of experiment 1} hours. 
The short, severed portion of Reissner’s fiber has not retracted 
backwardly. In front of the injury, however, the fiber has with- 
drawn forward completely out of the length of filum terminale exam- 
ined. Sections of a piece of spinal cord, taken from a region well 
forward in the trunk, reveal the fiber practically normal in size but 
lying slightly slackly and undulating. 
48. The incision was made at 4.45 p.m., August 19, and was fol- 
lowed by a very slight uplifting of the end of the tail, the lateral bor- 
