STimCTUnE AND DEVEEOPMENT OF REISSNER’s FIBRE. 27 
the occurrence of this phenomenon in Cyclostoraes and fishes. 
It will be obvious that the sudden recoil of the broken ends 
which normally occurs, and which results in the formation of 
a large coiled knot, must be of use^ in checking the further 
retraction of the broken fibre, for this knot blocks the 
comparatively small lumen of the canalis centralis, and, 
presumably, enables the fibre to establish a temporary hold 
until regenerative processes shall have restored its connection 
with the wall of the sinus terminalis. That regeneration 
does occur I have ample evidence to show (cf. Nicholls, ’12). 
'I’lie large percentage of cases in which the fibre is found 
broken and recoiled maybe due to the exception.ally strenuous 
exertions of the animals in their effects to avoid capture 
causing the fibre to snap. 
(d) Critical Discussion of the Views of Sargent 
and Houser. 
Before passing on to a detailed account of Keissner’s fibre 
and the sub-commissural organ in the several vertebrate 
groups, it will be necessary to discuss certain general 
statements made by Sai-gent, some of these being said to be 
confirmed by Houser. 
To the former author, and, though perhaps in a lesser 
degree, to Studnicka, is due the credit of having established 
the fact of the pre-formed nature of the fibre. Sargent 
further demonstrateil the constancy of its relation to the 
anterior part of the roof of the mid-brain, but, unfortunatel}", 
file mistakes in his earlier papers (’00, ’01) (especially those 
consefpient upon his failure, at that time, to recognise the 
posterior commissure, which, as I have shown above, he 
su{)po.sed to be the torus longitudiiialis), have coloured 
all his later work, detracting greatly from its value; for, 
although subsequently both posterior commissure and torus 
longitudinalis were correctly identified (’03, ’04), and the 
> We 1 lave an analogy in tlie formation of a blood-clot operating to 
close a severed blood-vessel and so to check further blood-flow. 
