STllUCTURE AND DEVELOPMENT OE llKlSSNEll’s FIBRE. 11 
covers the torus and enters the brain substance (fig. 10). 
In Cynoscion and Salvelinus the fibre, after passing beneatli 
the membrane, may be followed for 100 /t or more before it 
breaks up.” The “ membrane” here referred to, in the light 
of his text-fig. 1, is iudubitably tliat well-defined tract of 
highly modified ependymal epitlielium beneath the posterior 
cotnmissure for which the name “ sub-commissui’al organ ” 
has been recently suggested (Dendy and Nicholls, ’10). 
Sargent further seems to have confused the cavity of the 
mid-brain with the third ventricle, for he says (p. 39) : “As 
already stated, Reissner’s fibre extends through the whole 
length of the canalis centralis of the cord and continues 
cephalad through the fourth and third ventricles to the 
anterior end of the optic lobes.” 
In an appendix to this paper he controverts Studnicka’s 
( 99) statements (pnblislied six months earlier), and reaffirms 
his own opinion that Reissuer’s fibre is a pre-formed structure 
of a nervous nature. 
His conclusions were criticised by Kalberlah (’00) in the 
same year. This author figures Reissner’s fibre in a trans- 
verse section of the spinal cord of an embryo of Acanthias, 
and from a study of the condition of the fibre in that embi’yo 
he comes to the conclusion that it is an aitifact. It is quite 
possible that what he describes as “ eine gauze Kollektion 
soldier Fadenquerschnitte ” was simply a tangled mass of 
fibre, which might easily present such an appearance in 
transverse section.^ 
Although he actually quotes the sentence from Sargent’s 
paper in which that author refers to the posterior commissure 
under the uame “torus,” Kalberlah appears not to have 
noticed either this or other errors in Sargent’s work, to 
which I have here called attention. Sargent subsequently 
(’04, p. 135) dismissed Kalberlah’s criticism as valueless, 
remarking that that author had probably himself not seen 
‘ I have seen appeiirunees precisely similar to that figured by 
Kalberlah in sections of the spinal cord of the mouse in which a 
tangled heap of Reissner's fibre was cut through. 
