STRUCTUliE AND DEVELOPMENT OF REISSNER’s FIRRE. 9 
(three species)^ Auguis fragilis, Pygopus sp.^ Hinulia 
sp., Tropidouotus iiatrix, Emys sp.^Testudo stel- 
lata, Splienodoii punctatus (adult and embryonic). 
Aves. — Gallus domesticus and Columba livia. 
Mammalia. — Talpa europma, Erinaceus europieuSj 
Mus inusculus, l\Iicrotus arvensis^ Lepus cuniculus, 
Caviacobaya, Felisdomestica(?),AntliropopithecuSj 
and Homo. 
(b) Historical Review. 
So very complete a survey of the work of the earlier 
investigators who have noticed Reissner’s fibre and related 
structures has been given by Sargent (’04) that it will be 
necessary for me here to do little more than consider the 
more recent papers which refer to this subject, most of which 
have appeared since Sargent’s preliminary paper (’00). 
It is now a little more than fifty years since Reissner (’60) 
announced his discovery of the fibi'e Avhich bears his name. 
He described it as a fine cylindrical rod lying freely in the 
canalis centralis of the spinal cord in Petromyzon, but he 
did not ascertain either its origin or ending. He believed it 
to be a pre-formed structure of a nervous nature. 
For nearly forty years after its discovery the fibre remained 
strangely neglected, and of the comparatively few observers 
Avho mention its occurrence the greater number saw it only 
in the canalis centralis of the spinal cord, and appear to 
have agreed with Stieda (’68, ’73) that the structure was an 
artifact resulting from the coagulation of the cerebro-spinal 
Iluid under the action of certain fixing reagents. Sanders 
(’94) deserves notice as being the first observer to trace the 
fibre forwards (in Mjxine) into the Cavity of the mid-brain, 
and backwards into the sinus terminalis. Mayser (’82), 
with whose work Sanders appears to have been unaccpiainted, 
had ])revionsly found the fibre in the fourth ventricle of 
Teleosts. 
A new era in the study of Reissner’s fibre may be said to 
