o 
•ORORGE E. NTOnOLLS. 
PAOE 
Critical Discussion . . . . 7fi 
(a) The Sub-commissnral Organ in the Adult . 70 
(1)) Dev'elopinent ot the Sub-coinmissnral Organ 
and Reissner's Fibre . . . .78 
(o) Reissner's Fibre in the Brain-ventricles . 81 
(d) The Sinus terminalis . . . 8t 
(e) Reissner's Fil)re in the Sinus terminalis . 85 
IV. Reissner's Fibre and the Sub-commissural Organ 
IN THE MyXINOIDEI . . .88 
Bdellostoma (Polistotreina) stouti . !H) 
Bdellostonia cirrhatum . . !t8 
Myxine glutinosa . 1)8 
Critical Discussion . .10.8 
V. Reference List of Literature .108 
VI. Explanation of Plates . . .112 
I. Preface. 
In October^ 1907, when working in the Zoological Tjaborn- 
tory of the Imperial College of Science and 'i’ochiiology, I 
undertook, upon the suggestion of Professor Dendy, an 
investigation into the structure known as Iloissiier’s fibre. 
Since January, 1908, the work has been carried on in the Zoo- 
logical Department at King’s College (University of London). 
At that time the several papers which had been published 
some years earlier by Porter E. Sargent, in which he had 
announced his ''optic reflex theory,” had attracted coiusider- 
able attention, and his theory had been accepted by the 
authors of several text-books, notwithstanding that his 
results had not received adequate confirination. In view of 
the very remarkable character of his observations and his 
deductions tlicrefrom, confirination appeared desirable, and 
accordingly I set out to examine the fibre in a nnniber of 
vertebrates. Prom the very outset, however, I found that 
in several important, and, indeed, fundamental particulars, 
my observations differed markedly from those recorded by 
Sargent. I have accordingly refrained from publishing any 
account of my work until, from an examination of a very large 
