42 
GEORGE E. NICHOLES. 
The very delicate strands often to be seen in the canal is 
centralis, that seem to connect the fibre of Reissner with 
the ependymal epithelium, are evidently the “axons” which 
are supposed to pass out with the ventral roots of the spinal 
nerves to the musculature (’04, pp. 188, 195). 
According to Honser (Text-fig. 4, a), the stratum 
medullare profundum, which immediately overlies the 
“ Dachkern ” is a fibre system into which he claims to have 
“traced fibres from the cord and oblongata, fibres from the 
optic nerve, from the neurones of the tectum mesencephali 
itself. ... a great tract sweeps into it from the 
interbrain as a relay in the olfactory apparatus. Fibres are 
also present from certain of the cranial nerves. All of these 
fibre systems are to become related to the remarkable 
mechanism of Reissner’s fibre” (’01, p. 125). 
Houser thus suggests the transmission along the short cut 
provided by Reissner’s fibre of motor impulses consequent on 
sensory stimuli other than optic and olfactory, but he indicates 
paths quite different from those described by Sargent by 
whicli the sensory stimuli reach the cells of the “ Dachkern.” 
For although he concludes — “ It iscertainly evident that there 
are here every means for inter-communication between 
different parts of the nervous system,” yet he traces a con- 
nection between this stratum medullare profundum and 
the cells of the “Dachkern,” not as Sai-gent does, but by the 
passing of some of the fibres from the stratum medullare 
profundum itself down to the “Dachkern” there to end in 
arborisations over those cells. 
It will thus be evident that the two explanations of the 
working of this optic reflex apparatus have very little in 
common, and it is, indeed, rather suprising to find Sargent 
citing Houser as confirming his results. 
Moreover, I am quite unable to discover upon what grounds 
either Sai’gent or Houser have assumed the motor character 
of these “ Dachkern ” cells, for there appears to be absolutely 
no warrant for the assumption. 
It is myown opinion that these large cellsforming the “roof 
