174 GEORGE E. NICHOLLS 
Finally, it was captured and a close scrutiny revealed a slight 
external injury to the hinder margin of the caudal fin, which 
had a frayed appearance and from which a narrow strip of 
tissue (including the extremity of the filum terminale) had been 
scraped away. In sections subsequently prepared, it was seen 
that the sinus terminalis and the hinder end of the terminal 
filament were wanting. Reissner’s fiber had evidently been 
broken and had, doubtless, undergone a very considerable re- 
traction, but at the time the material was preserved the fiber 
had returned almost to normal size and stretched backwards to 
the damaged end of the terminal filament. For the most part, 
it lay in a fairly even course but near the actual end it was 
slack and lay in gentle undulations. The central canal appar- 
ently opened freely to the exterior and there were no signs of the 
formation of a new secondary sinus terminalis. 
During the following summer, several specimens (both rays 
and dogfish) exhibiting the reaction (of an abnormal attitude in 
repose) which is associated with the broken and retracted con- 
dition of the fiber were taken from the tanks of the aquarium. 
A piece of the tail (including the terminal portion of the 
central nervous system) of several of these specimens and, in 
some cases, a piece also of the spinal cord, or the brain, were 
sectioned. 
The first of these (Raia XIX) was brought in on August 2, 
the tail showing numerous abrasions obviously received in the 
trawl. The specimen was isolated and next morning was found 
showing a well marked reaction. Later that same day (about 
24 hours after its capture) it was killed and the nervous system 
exposed and preserved in the usual manner. 
In the sections, the terminal filament and sinus terminalis 
are found apparently undamaged but Reissner’s fiber had cer- 
tainly been broken, at or near the sinus terminalis. The free 
(broken) hinder end of the fiber was found near the sinus ter- 
minalis—almost brush-like (fig. 19). Traced forward from this 
point, the fiber is seen slack, swollen and snarled (fig. 25). 
It emerges from the anterior end of the tangle in a loosely 
coiled spiral, the twisted portion passing into a straight stretch 
