STRUCTURE AND DEVELOPMENT OF REISSNEr’s FIBRE. 57 
In the otlier series, a sagittal one, the sinus termi- 
nal is was cut obliquely. It appeared, however, to be a well- 
defined globular space. The anterior liemisphere was 
covered with the spreading flattened ependymal epithelium of 
the filum terminate, but this was lacking on the hinder 
half, and here the wall was made up wholly of couuective tissue. 
The sinus itself was filled with a granular coagulum and 
Eeissner’s fibre could not be identified. 
The effect obtained by a severance of cord and fibre when 
fixation is still incomplete has already been figured and briefly 
described by me (’09, ’12). The evenly twisted, condition of 
Reissuer’s fibre, to which I have referred as occurring in 
those cases where only a gradual recoil of the fibre has taken 
place, has been observed in the central canal of three different 
specimens of Petromyzon fluviatilis. 
The first case of this kind was obtained in the terminal 
portion of the spiual cord, which had been dissected out from 
the vertebral canal after partial fixation. The cord and fibre 
were cut in frout and retraction of the fibre has taken place 
backwardly from that point. In the operation of dissecting 
out the piece of spiual cord, however, the siuus termi- 
nal is was destroyed and the fibre has also retracted forwards, 
but it appears probable that the retraction took place princi- 
pally from before backwards, for from the point where the 
fibre was cut the canalis centralis is empty of fibre for 
a space of nearly fourteen millimetres. The anterior part 
of the piece of fibre in question is almost perfectly straight 
and not greatly swollen. This straight course continues for 
nearly a millimetre and then the fibre appears thrown into a 
number of close, tightly wound, corkscrew-like coils which 
alternate with short straight stretches (fig. 16). Of these 
corkscrew-like coils some thirty occur in the hinder part of 
the fibre, which is altogether about three millimetres only in 
length. The number of turns in any one twisted length 
varies from four to fourteen, with an average of eight. 
Occasionally, however, a single turn is found in an otherwise 
straight piece. 
