STRUCTURE AND DEVELOPMENT OE REISSNER’s FIBRE. 89 
Bdellostoma will relate to B. stouti unless otherwise 
expressly stated in the text. 
Of Myxine glutinosa I have had a dozen entire speci- 
mens, but of these only two were preserved with any care, 
being put entire into strong formalin immediately after their 
capture. The remainder were simply thrown into spirit and 
had almost certainly been dead for some time before pre- 
servation. 
It has been remarked by several writers who have dealt 
Avith the morphology of the central nervous system of Myxi- 
noids that there is an extraordinary range of variation to be 
met with in the brains of different individuals. This, my 
own observations, made upon eight Myxinoid brains, quite 
co>'ffrm. 
In particular, this variation is most marked in the extent 
to which the brain-ventricles have become reduced. In some 
specimens the cavities of the brain are relatively spacious, 
while in others they are enormously reduced, and in parts 
even altogether obsolete.^ 
'I'hose portions of the lumen of the brain which ai-e 
traversed normally by Reissner’s fibre are, however, least 
variable and are never wholly obliterated, a fact, I believe, 
not Avithout considerable significance as to the importance 
of that structure. 
Aly conclusions as to the homologies of the cavities of the 
mid- and hind-brain agree very nearly Avith those already put 
forAvard by Sterzi (’ 07 ). d’hey Avere, however, arrived at 
quite independently, and Avei'e based principally upon a 
consideration of the relations of Reissner’s fibre and the 
sub-commissural organ, to Avhich Sterzi, Avhose Avork came 
into my hands only recently, ap])arently makes no reference. 
Indeed, it is a sui-prising fact that of the several Avorkers Avho 
have concerned themselves with the histology of the Alyxinoid 
‘ Tills may result, I believe, from a continuance late into life of the 
process of thickening of the walls of the brain, their apposition and 
fusion, the differences obserA'ed then being merely a matter of age. 
