120 GEORGE E. NICHOLLS 
fact. He suggested that the alleged fiber was produced by the 
coagulation of the cerebro-spinal fluid under the action of the 
fixing reagent, pointing out that there was no evidence of its 
being related to any nerve cell. 
For thirty years this view passed almost unquestioned, Viault 
(76), Rohon (77), Sanders (’78, 794) and Gadow (’91) all ac- 
cepting it. More recently Kalberlah (’00), Streeter (03) and 
Edinger (08) have expressed themselves in agreement with 
Stieda’s view. That this view was so widely held is, doubtless, 
the explanation of the fact that during this period there are found, 
in the literature, so few references to the occurrence of the fiber. 
3. Interest in this structure revived, however, when Stud- 
ni¢ka (’99) reasserted the preformed nature of the fiber. This 
author suggested that it was to be regarded as an epithelial se- 
cretion, comparable to that which has produced the crystalline 
style of the lamellibranch gut. He believed that it is produced 
by the cells lining the central canal of the spinal cord and that 
it is capable of growing forward, to end freely in the brain ven- 
tricles but he made no suggestion as to its function. Kolmer 
(05) appears to be the only author who has endorsed this view 
and Studniéka has, himself, since abandoned it (713). 
4. It is a very surprising fact that the extraordinary and quite 
conspicuous development of the epithelium beneath the posterior 
commissure, should have remained for so long unnoticed. A 
brief mention of it, indeed, appears to have been made by Fulli- 
quet (86) but not until 1892 was it figured (very diagrammati- 
cally) by Edinger (’92) who conjectured that it might be a 
glandular body producing some secretion to be discharged into 
the cerebro-spinal fluid. Its histology was first carefully de- 
scribed by Studni¢ka (’00) who gave figures of its finer anatomy 
in dogfish and lamprey but did not, apparently, realize its con- 
nection with Reissner’s fiber. 
5. A little later the sub-commissural organ of the Ammocoete 
was described and figured by Dendy (’02) who noted the exist- 
ence of close-set cilia clothing its ventricular surface and sug- 
gested that, in conjunction with certain folds of the choroid plexus 
