No. I.] THE CRANIAL NERVES OF AMPHIBIA. 103 



species of Rana in the late larval stages of development. Other 

 Amphibia, especially the Amblystoma larvae, are brought in 

 incidentally as throwing light upon certain points. 



This research was begun at Princeton in 1889 at the sug- 

 gestion and under the direction of Prof. Henry F. Osborn. A 

 summary of the results first obtained appeared in the Zoolo- 

 gischer Anzeiger, Nr. 348, 1890 (61). At the Lake Laboratory, 

 established by Mr. Allis at Milwaukee, I was enabled to make 

 some additions to these results, which appeared in the Anatom- 

 iscker Anseiger, Nr. 15, 1892 (62). The final publication has 

 been delayed, owing partly to other duties and partly to further 

 observations made while Fellow in Biology at Columbia College, 

 and also during the past year. 



I wish to express here my deep indebtedness to Professor 

 Osborn for many valuable suggestions and for his assistance in 

 many ways in this research. For the execution of the majority 

 of the drawings I am indebted to Dr. Arnold Graf, to whose 

 skill they bear witness. 



L Technique. 



A considerable part of the investigation was upon tadpoles 

 fixed in Perenyi's fluid, stained m toto in carmine, imbedded in 

 paraffin and cut in serial sections. These were mounted in 

 order upon large glass slides, strips of thin mica being used as 

 covers. The carmine staining is not to be highly recommended, 

 as carmine solutions do not stain very differentially, and would 

 probably be even more unsuitable with forms where the tissues 

 are more compact than in the tadpole. 



The osmuim-bichromate mixture used for hardening in the 

 Golgi method gives in itself a very good stain for the medul- 

 lated fibres of the peripheral nerves, and sections prepared by 

 means of this method were thus doubly useful. 



The Golgi Method. — For the terminations of the nerves and 

 for demonstrating certain tracts consisting of many non- 

 medullated fibres, the Golgi method proved invaluable. It may 

 be well to describe here in detail the precise procedure which 

 I have found useful and convenient. 



