THE FUNCTION OF REISSNER’S FIBER 145 
have found produced as the result of my experiments (12, 
text-fig). 
Be the reason for this variation in position what it may, it 
has a certain importance in this investigation, for in one or two 
cases where the sinus terminalis lay unexpectedly far forward, 
the incision (which was made in the postero-ventral region of the 
tail, being planned to break the fiber actually in the sinus ter- 
minalis) missed the terminal filament altogether. 
Of young dogfish, only recently emerged from the egg-case, I 
have had no material but in the adult there appears to be little 
variation in the position of the terminal sinus. 
In several cases, both dogfish and rays, the cut was made in 
the region of the terminal filament but just a trifle too far dor- 
sally, and the sections show that, although the cut penetrated 
the neural canal, the filum terminale and surrounding pia mater 
escaped damage. 
Such specimens in which the experimental incision failed to 
break the fiber served well as control specimens. Other control 
specimens were simply anaesthetized without undergoing the 
usual operation. These latter on recovery behaved in perfectly 
normal manner. 
IV. OBSERVATIONS UPON THE LIVING ANIMAL 
1. Upon normal material 
The experiment carried out in 1910 had almost immediately 
directed my attention to the fact that a frequent, if not an invari- 
able, consequence of the operation was the assumption by the 
subject of the experiment of a very distinct attitude while at 
rest. Accordingly, during the time spent at Plymouth both in 
1910 and 1911, while the experiments were going on in the 
Jaboratory, very constant and careful attention was given to the 
numerous normal specimens which were kept in confinement in 
the adjoming aquarium. Control specimens, too, were kept 
under observation in small tanks in the laboratory under condi- 
tions precisely similar to those in which the subjects of the 
experiments were maintained. 
