THE FUNCTION OF REISSNER’S FIBER 121 
of the midbrain, it served to establish currents which promoted 
the circulation of the encephalic fluid. 
6. In the meanwhile Sargent had also asserted the preformed 
nature of Reissner’s fiber but had denied that Studni¢ka was cor- 
rect in interpreting it as a secretion. In Sargent’s view the fiber 
was a nervous structure. 
In several subsequent papers (’01, ’03, ’04) Sargent endeay- 
ored to establish this view stating that Reissner’s fiber consists 
of ‘‘numerous axis cylinders closely applied to each other and 
surrounded by a single thin medullary sheath of myelin.” These 
axis cylinders were supposed to be derived in part from the nu- 
merous large cells of the ‘Dachkern’ and from alleged multi- 
polar cells in the habenular ganglion as well as from other mul- 
tipolar cells said to be situated actually within the lumen of the 
central canal, towards the hinder end of the spinal cord. In 
teleosts, in which group Sargent overlooked the remnants of the 
‘Dachkern,’ he claimed that the alleged midbrain constituent 
“axons” of Reissner’s fiber were derived from the myriad 
cells of the torus longitudinalis. 
Reissner’s fiber was, therefore, according to this author, built 
up of two sets of axons running in opposite directions and a 
comparison was made between this structure and the giant fibers 
of Amphioxus and Annelida. Concerning the destination of the 
forwardly running axons there is nothing stated, but those which 
were said to arise in the brain were regarded as motor axons 
having a very great length, each being supposed to stretch from 
the midbrain roof direct to one of the trunk muscles. Sargent 
stated that he had seen such fibers leaving the main Reissner’s 
fiber in the region of the spinal cord and that these passed out 
directly to the musculature, probably by way of the ventral 
spinal roots. In the midbrain roof the related nerve cells were 
described as in direct connection with the proximal ending of the 
retinal neurons so that there was said to be interposed but a 
single nerve element between the sensory (retinal) nerve cell 
and the muscle-fiber in the trunk. Sargent suggested that, by 
this means, the delay in the transmission of motor stimuli along 
