THE FUNCTION OF REISSNER’S FIBER 16} 
was not one which I should be inclined to describe as ‘marked’ 
it was, nevertheless, too considerable to be attributed to the 
scarcely appreciable retraction which has occurred at the severed 
end of the fiber. 
If, then, I am correct in regarding the occurrence of this ex- 
ceptionally delicate fiber as indicative of an early stage in a new 
backward growth of the fiber after some unusually extensive re- 
traction, the reaction noticed in these two experiments may 
perhaps have been the consequence of a renewed disturbance of 
the Reissner’s fiber mechanism in specimens in which the repair 
of a previous disturbance had scarcely been completed. 
The condition of Reissner’s fiber in the subjects of these eight 
experiments may therefore be summed up as follows. 
One (19) is to be regarded as exhibiting a slight retraction 
of the fiber started at the moment of fixation of the material and 
quickly checked; two others (9, 39) showed a considerable re- 
traction resulting from an accidental cutting of the fiber during 
the dissection made to expose the central nervous system. ‘The 
remainder are regarded as showing stages in the retraction (or 
repair) of the fiber consequent upon a breaking of the fiber prior 
to the experiment. This snapping of the fiber may have oc- 
curred immediately (8, 49) or some little time (70) or some con- 
siderable time (46, 55) before the incision was made. ‘That such 
a breakage of the fiber does occur not infrequently in life and 
that it may produce a reaction comparable to that induced by 
artificial section of the fiber will be seen from the account given 
in the following section. 
2. Non-experimental material 
An attitude similar to that induced in many specimens by the 
experimental incision, was occasionally noticed in specimens (not 
the subjects of the experiments) confined in the aquarium of the 
Plymouth Biological Station. 
Of these, one—a dogfish (F)—was obtained during the sum- 
mer of 1910. It had been seen in the aquarium at intervals 
extending over several days with both head and tail well up. 
