52 CHARLES BROOKOVER 



either formalin or alcohol fixation. Toluidin blue gives a more 

 brilliant stain than methylen blue and is easier to control, as it 

 does not diftentiate so rapidly in the alcohol. Neither does it 

 seem to fade so rapidly afrer the sections are mounted in balsam. 

 Methylen blue was used intra- vitam by injecting it through the 

 ventral aorta. One half of one per cent solution in distilled 

 water was kept in stock and mixed with ten times its bulk of 

 normal saline solution at the time of using. Chemically pure 

 sodium chlorid was used with Griibler's Bx brand of methylen 

 blue. The method employed was, in the main, the one used by 

 Wilson ('04). Pieces were cut out and examined under the com- 

 pound microscope to determine when impregnation had taken 

 place. The pieces were kept in the ice box while in the ammon- 

 ium molybdate and in the alcohols. This gave better results on 

 the peripheral than on the central nervous system. 



I wish to thank the Ohio State Academy of Science for a sub- 

 stantial contribution from the McMillin fund toward defraying 

 the expense for material. I am much indebted to Mr. Alex. 

 Nielsen of Venice, O., for furnishing me adult fishes fresh from 

 his nets and to Prof. Herbert Osborn for facilities for working 

 and gathering material while at the Ohio State University Lake 

 Laboratory on Lake Erie during three summers. I am also under 

 many obligations to Prof. C. Judson Herrick for generous con- 

 tributions of literature loaned or donated, as well as for his 

 friendly advice and criticism while engaged in the work. 



HISTORICAL SKETCH 



In 1862 Max Schultze showed that the nucleus of origin of the 

 olfactory neurones of the first order lies peripherally in the ol- 

 factory epithelium. Since that time his results have been con- 

 firmed by various workers repeatedly. Bedford ('04) gives a 

 brief summary of some of the more important papers, — espe- 

 cially those of an embryological nature. His resume of the liter- 

 ature shows that the older embryologists were of the opinion that 

 the olfactory nerve arises centrally. Then views changed after 

 the appearance of the paper of His, Jr., in 1889, showing that in 



