THE FUNCTION OF REISSNER’S FIBER 147 
ledge and the tail projecting out stiffly. This is not to be attrib- 
uted to a natural rigidity of the tail, for this region of the body 
is peculiarly flexible, and it must be assumed that the posture is 
maintained by muscular effort. 
At times, however, dogfish will wedge themselves into crevices 
between the rockwork in a nearly vertical position, but even then 
they maintain a posture in which the long axis is approximately 
straight. 
As will appear, a quite different attitude is assumed by speci- 
mens in which the fiber of Reissner has been accidentally or 
otherwise injured. Indeed, specimens which have received in- 
jury resulting in the breaking of the fiber can be easily recog- 
nized by the attitude in which they rest. 
The normal attitude of the rays is strictly comparable to that 
just described for dogfish. These animals will, in confinement, 
settle, apparently indifferently, either upon a horizontal or a 
smooth vertical surface. While, however, the rays may often be 
seen adhering to the smooth surface of the wall of the tank, or 
the glass front of the tank, they appear unable to maintain 
themselves for long in this position. In the larger tanks and 
aquaria they seem to exhibit a preference for smooth and level 
horizontal surfaces. 
In either case the whole ventral surface (including that of the 
head and flattened tail) is applied to the supporting surface 
(fig. 7). The snout, it is true, may be very slightly lifted from 
that surface (fig. 10). The flexible tail stretches backwards, its 
long axis being a continuation of that of the trunk. 
2. Upon experimental material 
I propose, here, to give a general outline of the reaction ob- 
served in the subjects of the experiments in order that the sig- 
nificance of the various experiments, a detailed account of which 
is given in the succeeding section, may be more readily appre- 
ciated. 
In the subject of the experiments, recovery from the anaes- 
thetic occurred usually within a very few minutes and was fre- 
