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 w^as 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 



