THE FUNCTION OF REISSNER’S FIBER 123 
Ayers never saw Reissner’s fiber in the lamprey, since his de- 
scription of the ‘ventricular fibers’ in that animal as ‘‘a fine- 
meshed network of fibrils which . . . . in life practically 
fills the ventricular cavity”’ certainly can not apply to Reissner’s 
fibers. It is extremely probable, therefore, that Ayers failed 
to distinguish clearly between coagulum and the fibrillae of 
Reissner’s fiber. His conclusion that the fiber was certainly 
“an organ of relation bringing all parts of the ventricular cavity 
into. intimate connection”? (my italics) is likewise mistaken, for 
Ayers did not correctly identify the brain cavities in this animal, 
in which of the iter little remains but the sub-commissural canal. 
Accordingly he failed to recognize the distinction which exists 
between the tract of modified epithelium which constitutes the 
sub-commissural organ and the flattened epithelium which 
lines other parts of the ventricular cavity. Concerning the 
function of the fiber he conjectured that it might be ‘‘ connected 
with the control of the ventricular lymph supply by vaso-motor 
control.” 
9. Horsley (08) describing the occurrence of Reissner’s fiber 
in certain apes stated that, in these forms at least, the fiber 
had not the structure of a tract of nerve fibers nor, when cut, 
did it exhibit Wallerian degeneration. While not denying the 
accuracy of Sargent’s statements in so far as they relate to this 
structure in the lower vertebrates, Horsley expressed the opinion 
that, in its resiliency, the fiber resembled a chitinous or skeletal 
structure and suggested that, in the higher vertebrates, it had 
become nothing more, perhaps, than a residual structure. 
10. In 1909 I gave an account (’09) of the behavior of the 
fiber in recoil and stated that, in my opinion, the fiber was cer- 
tainly non-nervous. At the same time Dendy (’09) put for- 
ward an entirely novel suggestion concerning the function of 
the fiber. His suggestion was that the fiber itself was a strand 
of connective tissue which played a merely mechanical part, 
variations in its tension being produced by the flexure of the 
body and every such variation might be supposed to result in a 
stimulus being transmitted to the cells of the sub-commissural 
organ This latter structure was interpreted as a sensory 
