ir 
A third matter upon which information was sought was that of 
the manner in which this regeneration was effected. It was not known 
whether a tangle, once formed, remained as a permanent result of the 
breaking of the fibre or, if it were transient, whether it might simply 
uncoil or whether the whole fibre or the tangled part of it disappeared 
to be replaced by new growth. 
These, then, were some of the problems to be solved, and although 
it cannot perhaps be claimed that the results obtained from my ex- 
periments have given a decisive answer to all of these questions, yet 
it is believed that they do, notwithstanding their acknowledged in- 
completeness, illumine certain aspects of this subject which were 
hitherto obscure and thus justify their publication at this stage. 
It is hoped that a complete solution of the problem may result 
from a further and more extended investigation which is about to be 
undertaken. 
V. Methods and Material. 
My discovery of the true relations of the sinus terminalis and 
REISSNER’s fibre at its posterior extremity suggested to me a practic- 
able way of setting about experimental work which would be free 
from the objections which have been urged against the experimental 
method adopted by SARGENT. The nearly complete absence of nervous 
tissue at the end of the filum terminale renders REISSNER’s fibre 
peculiarly accessible at that point. The almost exposed condition of 
the terminal filament in elasmobranchs and teleosts, coupled with the 
fact that in these two groups ReISSNER’s fibre has been stated (Sar- 
GENT, 1904) to attain its greatest development, determined the choice 
of material. 
My experimental work was carried out in the Laboratory of the 
Marine Biological Station at Plymouth during July of last year. I 
take this opportunity of acknowledging my obligations to the British 
Association for the Advancement of Science for the use of their table 
there and of expressing my thanks to Dr. ALLEN for the facilities 
afforded me for the prosecution of this research. 
Originally it had been intended to use the dogfish (Scyllium cani- 
cula) principally for this part of the work but it happened that small 
specimens of that animal were not readily obtainable at the time. 
Since nothing was known as to the probable extent of the recoil 
and new regions of the tail and in sections through both of these 
regions Rrissner’s fibre could be distinctly recognized, lying centrally 
in the lumen of the canalis centralis. 
