4 
GROltaE E, NIOHOELR. 
but also for most kindly undertaking the reading of tlie 
proofs. Further, he has placed at my disposal some valuable 
material, and allowed me the use of his large collection of 
slides. I wish also to express my thanks to Dr. Allen, 
Director of the Marine Biological Ijaboratoi’y at Plymouth, 
and to his staff, for the facilities afforded me for the collec- 
tion of material and for the carrying out of experimental 
work while occupying the British Association’s table there. 
For assistance in prociu’ing otlier of the material employed 
in this research I desire to express my obligations to 
Professor Meek, Dr. A¥oodland, and Mr. W. F. Allen, while 
to IMr. R. W. II. Row my thanks are dne for the greater 
number of the photomicrographs used in illustration, and to 
i\Ir. Charles Biddolph for assistance in the preparation of 
many of the series of sections. 
II. Introduction. 
(a) Methods and Material. 
In the brain and spinal cord of almost every specimen 
examined Reissner’s fibre could be recognised without diffi- 
culty. In a few instances only was it apparently absent, and 
this, practically in every case, in animals which had been 
preserved entire in fixing fluids of low penetrative power, or 
where, if the brain-case had been opened, as in some of the 
larger specimens, there had been insufficient exposure of the 
brain and spinal cord to the action of the fixing reagents. 
In the preservation of such of the material as I was able 
to obtain in the living condition a number of the commonly 
employed fixing reagents were tried. Of them all, the 
aceto-bichromate mixture (Bolles Lee, pp. 49-50), with 
which I had previously obtained satisfactory results on 
particularly refractory Teleo.st material, proved the most 
generally useful, and was latterly made use of almost exclu- 
sively, being found to combine fairly rapid penetrative 
powers with a good hardening action. With this fluid, too. 
