26 
GKORGE E. XICIIOLLS. 
of the coalescence of hypertrophied cilia, the fusion is so 
intimate that the whole fibre has a homogeneous glassy 
appearance. In favour, moreover, of such a view of the 
nature of the fibre is the extraordinary rapidity with which 
it disintegrates at death. It is practically useless to examine 
material for Reissuer’s fibre if that material has been dead 
for an hour or so before fixation, and further, even in matei-ial 
which has been fixed at death, but which is of sufficient size 
to prevent speedy peneti'ation, or even iu small itiaterial 
where a slowly penetrating fluid has been employed, it is rare 
to find the fibre preserved. In such cases the general 
ependymal cilia, too, have almost invariably disappeai-ed. 
Apart, then, from the doubtful existence of a delicate 
investing sheath, I have been unable to demonstrate !xny 
internal structure in Reissner’s fibre, even with the aid of 
very high powers of the microscope. It seems certain, never- 
theless, in view of the constancy of the mode of recoil which 
the fibre exhibits, that some very definite internal structure 
must exist. 
An explanation may perhaps lie in the manner of develop- 
ment and growth of the fibre. It may well be that when, in 
early development, the fibre (arising fiom fused .sub-com- 
missural fibrillEe) grows backwards to enter the canal is 
centralis, it is at once joined by siudlar fibrillm or cilia from 
the ependymal cells, which, overlying the earlier formed struc- 
ture, continue its backward growth. These, in their turn, 
would be continually covered by fresh accessions, and the 
entire fibre would I'esernble a species of “ hay-rope.” If the 
whole of these fibrillae have a slight spiral growth the manner 
of recoil of the fibre formed by their union would be easil}' 
understandable. Even the retention, to a certain extent, of 
their individuality by the fibrillae might in itself be sufficient 
for the spiral retraction. In all such cases of recoil, however, 
the fibre has torn itself free from its attachments. 
1 have already suggested that accidental breakage of 
Reissner’s fibre may occur not infrequently, peihaps, in life, 
and I have obtained a considerable amount of evidence of 
