98 
GKORGB E. NIOHOLLS. 
Ventrally it ends abrupt!}^, being quite sharply marked off 
from the epithelium of the sinus m es oc oeli cu s . 
'J'he actual cells of the sub-commissural organ are, like 
those of the Petroinyzontidae, extremely elongated and fibre- 
like. In both Bdellostoma and Myxine they attain a length of 
about 50 fi, or approminately half of the diameter of the 
sab-commissural canal. 
'riie fibrillae of Eeissner’s fibre spring most freely from the 
anterior portion of the organ, bat some continue to join the 
fibre along the whole extent of the sub-commissaral canal. I 
have not been able to detect any fibrillae arising from the 
epithelium which passes into the optocoel, thoagli it is not 
improbable that some strands may actually have their origin 
there. In one specimen, indeed, a very fine factoi' appeared 
to issue from the optocoel to join ReissnePs fibre. 
Bdellostoma cirrhatum. 
In the single series of sections through the brain of this 
species Reissner’s fibre can only be seen in some sections. 
The sections were ti’ansverse and very thick, and the fibre had 
doubtless fallen away (it being in thick ti-ansverse sections 
difficult to attach the sections of fibre sufficiently to the slide). 
The ventricles of the brain very closely resemble the con- 
dition described as occurring in that specimen of B. sto uti in 
which they had been least reduced. The cavity in the upper 
part of the hind-brain is relatively spacious and in open 
communication with the fourth ventricle. In the mid-brain 
there is a quantity of coagulurn which, both in the sinus 
mesoccelicus and in the ventricular canal, might be mistaken 
for tangled and netted masses of Reissner’s fibre. It was 
probably some such condition as this which misled Ayers 
(see i n fra). 
]\I y X i n e g 1 u t i n o s a . 
Of this species all but two of my specimens had been 
preserved entire in alcohol. As spirit usually jenetiates 
