40 
GEOHGE E. NICHOLES. 
prove to be almost entirely different from the account and 
explanation subsequently offered by Sargent. 
In order that these different accounts may be more readil}’^ 
compared I have, in 'J'ext-fig. 4, endeavoured to represent 
quite diagrammatically what is alleged by these two authors 
concerning the cellular connections of Reissner’s fibre. 
As I understand it, SargenRs view (Text-tig. 4, b) 
supposes that sensory stimuli (optical and olfactory) reach 
certain cells in the tectum mesencephali (those of the 
torus in Teleosts, and of the “ Dachkern ” in other verte- 
brates), and in the habenular ganglia. 'I’hese Dachkern” and 
torus cells are said to be multipolar, each being stated to give 
off (i) an “ axon,” which courses anteriorly to join Reissuer’s 
fibre; (ii) a “ neurite,” ultimately passing posteriorly into the 
cerebellum, there to “ end in fibrillations in the molecular 
layer” in direct contact with the processes of the Purkinje 
cells; and (iii) a process which makes its way “towards the 
ectal region of the tectum opticum,” to come “ directly in 
contact with the endings of the proximaily running fibres of 
the optic nerve. It is by this pi-ocess that the cell 
is put in direct connection with the outer world 
by the retina” (’04, p. 168) — the spaced type is mine. The 
“Dachkern ” ceils are clearly regarded as motor, for Sargent 
says that their axons “ pass by the shortest route through 
the venti'icle and canal to the posterior portion of the nervous 
sj'stem, where they pass into the cord and probably pass out 
through the ventral root to the musculature” (’01, p. 450). 
The habenular cells (which in Cyclostomes, at any rate, are 
said to be multipolar) also contribute axons to Reissner’s 
fibre, which thus serves “as a short circuit for the trans- 
mission of reflexes arising from olfactory as well as optic 
stimuli ” (’04, p. 162). 
Sargent also claims that the fibre growing backwards from 
this cephalic part of the apparatus fuses with “axons” extend- 
ing forwards from (motor ?) cells lying wholly within the 
sinus terminalis, but nothing is said as to the anterior 
ending of these latter axons. 
