410 
REISSNER’s fibre was, in any way, related to that structure nor did 
he make any suggestion as to the function of either body. He con- 
firmed SANDER’S account of a coiled mass of fibre in the terminal 
sinus in Myxine and supposed this coiled condition to be a normal one. 
SARGENT reverted to the earlier view that the fibre was a ner- 
vous structure and endeavoured to prove that it formed part of an 
elaborate optical reflex apparatus. He demonstrated a connection 
between REISSNER’s fibre and the sub-commissural organ (“Ependymal 
Groove”). 
In the autumn of 1907, at the suggestion of Professor DENDY, to 
whom I desire here to express my thanks for much valuable advice 
and criticism, I took up the study of this structure. A detailed ac- 
count of my investigations upon the nature and occurrence of Reıss- 
NER’s fibre and the associated sub-commissural organ is now nearly 
ready for publication and it must, therefore, be sufficient to state here 
that although it was impossible to entertain the slightest doubt of its 
preformed nature, my observations led me, almost at the outset, to 
disagree with SARGENT’s conclusions that REISSNER’s fibre was a nerve 
fibre or tract of nerve fibres. 
A brief general account of the fibre will, however, be included 
here in order that the nature of the experiments may be appreciated. 
II. REISSNER’s Fibre and its Relations to the Central Nervous System. 
The fibre itself is an exceedingly delicate thread with a very 
high refractivity and appears even under the highest powers of the 
microscope to be absolutely structureless. In life it exists normally 
under considerable tension and, if severed while fresh, the free ends 
commonly recoil sharply to form very characteristic knots or “snarls” 
(Pl. I, Fig. 3). I have already pointed out (1909) that such recoil is 
due to the essential elasticity of the substance of the fibre and that 
this elasticity is destroyed by the action of fixing fluids. Even when 
partially fixed, however, the resilience of the fibre is such that it will 
still contract, if severed. Under these circumstances, the contraction 
appears to be a comparatively gradual one and the fibre will then 
give rise to more or less regular spirals as figured by me in the case 
of Petromyzon fluviatilis (1909) and as now shown for Scyllium cani- 
cula (Pl. I, Fig. 6 R.f.). This retraction of the free end of the fibre 
thus differs markedly from the recoil of a simple (homogeneous) elastic 
thread in that it practically always takes on this spiral form. For, 
even where the recoil has been an abrupt one and a large knotted 
mass has resulted, a careful examination always discloses a spiral 
