STIJUCTURl!] AND DEVELOPMENT OF REISSNER’s FIBRE. 55 
centralis may thus be said to open freely by a terminal 
neur:il pore or foramen into the lympli-space that surrounds 
the cord. Through this terminal foramen Reissner’s fibre 
passes, to become iuserted into, and apparently confluent with, 
that portion of the meningeal sheath that forms the posterior 
wall of the sinus terminalis. Its insertion is in the middle 
line and upon the postero-ventral part of the wall of the sinus. 
In fig. 13 the fibre is seen passing across the sinus ter- 
minalis to its pointof insertion into thewallof that chan>ber, 
and in this instance the fibre shows only a slig’ht twisting at 
short intervals. In the other specimen (figs. 12, 40), the fibre 
is seen to pass into the apex of a conical mass {r.f.") of coiled 
fibre which lies against the ventro-posterior wall of the sinus 
and occupies a considei'able portion of its cavity. 
The descriptions of Stndnicka (’99) and of Sargent (’04), as 
well as my own earlier experience (Nicholls, ’09), had prepared 
me for a complete or partial recoil of the fibre in this region. 
In order to prevent this and to obtain, as far as might be, a 
representation of the actual condition in the living animal, 
considerable care was exercised in the preparation of the 
material. "With this end in view, two freshly killed lampreys 
were taken and immersed whole in the fixing fluid (aceto- 
bichromate), and, while so immersed, a short stretcdi of the 
skin and muscles was removed from one side of the tail to 
within about an inch from its end to allow of the belter and 
more speedy penetration of the sjiinal cord by the fixing fluid, 
without any i-isk of damage to, or displacement of, the spinal 
cord ami enclosed Reissuer’s fibre. This last inch or so of the 
tail was only cut off nearly an hour later, by which time it 
was supposed that the fibre had become well fixed and its 
elasticity destroyed. The tissue was then further hardened 
in the fi.xiug fluid for another twenty-four hours or more. 
In the case of specimen E subsequent examination of the sec- 
tions showed that there had been no post-mortem I'ecoil of the 
fibre, which could be traced forward uninterruptedly from the 
sinus terminalis in a perfectly straight line through the 
canalis centralis. It is thus practically certain that the 
