14 
r.EOROK E. NrCIIOELS. 
Sargent states also (’01, p. 4ol) that “in those species 
'which are totally blind no trace of this apparatus is to be 
found ” — an erroneous statement that has since found its way 
into several text-books, notwithstanding that, so long ago 
as 1894, Sanders had mentioned the existence of a particularly 
well-developed Reissner’s fibre in Myxine, his discovery being 
confirmed by Studuicka in 1899. 
In the latter part of the same paper Sargent gives an 
account of certain experiments performed upon living sharks, 
the operation consisting in breaking Reissuer’s fibre in the 
fourth ventricle. He states that he observed that “ those 
sharks in which the fibre had been broken showed a slowness 
in response to optical stimuli,” indicated by an inability to 
turn quickly to avoid obstacles interposed suddenly in their 
paths. This is construed as evidence that the breaking of 
Reissner’s fibre had interrupted the conduction of optical 
stimuli by the “short-circuit” path constituted by that fibre. 
I have pointed out elsewhere (’12) that the evidence afforded 
by these and other experiments is susceptible of another and 
much simpler explanation in accordance with Dendy’s sug- 
gestion (’09), to which I shall have to refer shortly. 
Later in the same year Houser (’01) published an account of 
the neurons and the supporting elements of the Selachian 
brain, his descriptions being based upon the study of adult 
Mustelus. In this memoir he repeatedly states that he 
found Reissner’s fibre arising as the product of the coalescence 
of paired fibre-tracts, the constituent fibres of which were 
the axons of the cells of the “ Dachkern,” or roof nucleus. 
This account of the fibre in Mustelus agrees closely with 
the condition in Selachians as at that trine described by 
Sargent from a study of the embryo of Raja, but differs in 
an all-important particular from the account of the fibre in 
Mustelus and Selachians generally as given subsequent!}’’ 
by Sargent (1904), when the fibre was (correctly) clesci'ibed 
as continuing forwards beneath the posterior commissure. 
Houser apparently did not notice (as, indeed, extraordinary 
as it may appear, no subsequent observer seems to have done) 
