124 GEORGE E. NICHOLLS 
organ, controlling automatically the flexure of the body. He 
concluded by expressing the hope that some way would be found 
of overcoming the apparently insuperable obstacles which stood 
in the way of satisfactory experiments upon the fiber by which 
alone could the hypothesis be tested. 
11. A study of the development of Reissner’s fiber in Cyclo- 
stomes (and Amphibia) led me to the conclusion (712, ’12a, 713) 
that this structure was formed by the coalescence of cilia-like 
processes springing from cells which, while largely collected 
upon the sub-commissural organ, are not limited to that organ, 
other cells occurring scattered in the ependymal lining of the 
central canal contributing to the fiber. In my opinion, the 
fiber is to be regarded as a thread of protoplasm. This view 
is supported by the staining reactions of the fiber, while its 
high refractivity, its power of regeneration and the rapidity 
with which it apparently disintegrates after death are facts 
easily explicable upon this hypothesis. Further, its mode of 
contraction is paralleled, only, so far as I am aware, in the 
searcely modified protoplasm which forms the stalk of certain 
Protozoa. 
This view that the fiber is, in fact, a protoplasmic thread 
has since been accepted by Dendy (’12), Studnicka (713) and 
by Tretjakoff (13). The latter author, however, appears to 
have misread Sargent’s papers, for he attributes this view to 
that investigator, saying (’13, p. 110) “Sargent zeigte namlich, 
dass der Faden noch in embryonalen oder larvalen Leben als 
ein Bundel von feinen, cilienahnlichen Fortsatzen der Zellen 
der Sub-kommissuralen Grube ensteht.”’ 
12. Tretjakoff (’13), however, while accepting this view of 
the nature and function of the fiber suggests that we are mis- 
taken (‘“‘ich glaube deswegen, dass in diesem Punkt die ‘Theorie 
von Dendy und Nicholls falsch ist’”’) in attributing any sensory 
function to the sub-commissural organ. He believes that the 
sensory cells connected with Reissner’s fiber are found only in 
the epithelium which lines the central canal and holds, with 
Sargent, that the sub-commissural organ serves merely for the 
support or anchorage of the fiber. These sensory cells are 
