MULLENIX: EIGHTH CRANIAL NERVE. 221 
gators concluded that the union of sense cells and axis cylinders is 
secondarily established by the development of the extraordinary 
protoplasmic bridges. 
III. Material and Methods. 
The ear of the fish affords superior material for the investigation of 
this problem, in that gross anatomical conditions are less complex 
than in the higher vertebrates, and orientation is therefore simpler. 
Furthermore, owing to the absence of a bony labyrinth the terminal 
nervous structures are much more easy of access for chemical reagents, 
and complete series of sections are more easily obtainable than in 
other vertebrates. The fish chosen was Fundulus heteroclitus, the 
common “ Killifish,” or “‘Mummichog” of the Atlantic coast. ‘The 
work has been done at the Zoological Laboratory of Harvard Univer- 
sity, under the supervision of Professor G. H. Parker, to whom I am 
indebted for the inspiration, stimulating suggestiveness, and helpful 
criticism which characterize his teaching. 
A large number of preparations was made by the older neurological 
methods before a process was found which differentiated the nervous 
from the non-nervous material of the organ. The Golgi multiple 
method, methylene blue, gold chloride, Vom Rath, and other methods, 
were resorted to, but without success. Likewise, the photographic 
reduction process devised by Ramon y Cajal was tried, but no impreg- 
nation was secured. Finally, resort was had to Bielschowsky’s (:02, 
:03) formaldehyde method for the reduction of silver oxide, a method 
which has proved useful for the study of central organs. A large 
number of successful impregnations was obtained, and these prepa- 
rations furnished the material represented in the accompanying 
drawings and constitute the basis for the conclusions arrived at. 
In preparing the organ for histological treatment the head of the 
living fish was severed from the body, an opening was cut in the dorsal 
wall of the cranium to facilitate the entrance of the killing fluid, and the 
head thus prepared was dropped into a 12 % solution of formalin 
(40 % formaldehyde). Heads were allowed to remain in this fluid 
for at least 24 hours. Bielschowsky states that material may be 
preserved in it for several months, or even a year, and still give good 
results. An occasional renewal of the fluid is advisable. 
After fixation and preservation in formalin the heads were split 
along the median line, and each half-brain, with the corresponding 
