112 
CxEORGE E. NICHOLES. 
EXPLANATION OP PLATES 1-5, 
Illustrating Prof. George E. Nicholls’ paper on “The Structure 
and Development of Reissner’s Fibre and the Sub-com- 
inissui'al Organ.” — Part I. 
List of Reference Letters. 
c. bg. Corpora bigemina. c. c. Canalis centralis of the 
spinal cord. c. c.' Upper canal of canalis centralis (in Myxinoids). 
cil. Cilia. Dk. Cells of the “ Daclikern.” e. ep. Ependymal epithelium. 
ep. Epiphysis. fh.,fb.' Fibrillae of Reissner's fibre, h.g. Habenular 
ganglion, i. c. Isthinic canal, inf. Recessus inf rapinealis. iter. 
Iter. myig. Meninges, m. r. Mesoccelic recess, m. t. Cells of the ter- 
minal mass. nch. Notochord, n.p.c. Nucleus of the posterior com- 
missure. op. Optocoel ; optocoelic canal (Myxinoids). op.' Posterior 
extension of optoccelic canal, p. c. Posterior commissure, r. d. Dia- 
coelic recess, r.f. Reissner’s fibre, r.f.' Reissner’s fibre, tangled in 
canalis centralis, r.f." Reissner’s fibre, tangled in sinus ter- 
minal is. s. c. Spinal cord. «. c. c. Sub-commissural canal, s. c. o. Sub- 
commissural organ. s. m. Sinus mesoccelicus. s. m.' Upper 
chamber of sinus mesoccelicus. s.m.'' Lower chamber of sinus 
mesoccelicus. e. t. Sinus terminalis. t.c. Tela choroidea II. 
feet. wes. Tectum mesencephali. <. p. Terminal plug. v.c. Ventri- 
cular canal, x. Large space (part of fourth ventricle) in roof of hind- 
brain, lying above the canal-like fourth ventilcle. III. Third ventricle. 
IV. Fourth ventricle. * Indicates the position of the extremity of the 
notochord in Fig. 52. 
[Figs. 1-32 are all reproduced from photomicrographs ; the remaining 
figures, 33-58, were drawn from the actual preparations with the aid of 
a camera lucida.] 
PLATE 1. 
Figs. 1-9 represent the sub-commissural organ of typical members 
of the different vertebrate sub-classes, as seen in transverse sections of 
the brain. 
Fig. 1. — Petromyzon fluviatilis. x 28. 
Fig. 2. — Raia bland a. X 65. 
Fig. 3. — Scyllium canicula. x 24. 
