180 PROCEEDINGS OF THE AMERICAN ACADEMY. 



some degree the method adopted by Strong ('95), it has seemed possible 

 to make out more accurately the homologies of Urodelan and Anuran 

 nerves than has before been done. 



The color scheme used by Strong has been followed as closely as 

 practicable ; roots and ganglia, however, have been left neutral from 

 lack of knowledge of the exact proportions of the different components 

 passing through the ganglia. Strong's nomenclature has also been 

 adopted, since it proves quite as applicable to the Urodelan as to the 

 Anuran type. The confusion which would have arisen from the use of 

 two or more sets of terms is thus avoided. 



My work has been carried on in the Radcliffe College Laboratory at 

 the Museum of Comparative Zoology, Cambridge ; and it is with great 

 pleasure that I acknowledge here my indebtedness to the Director of the 

 Laboratory, Professor E. L. Mark, who has assisted and advised me, and 

 helped me in many ways. I also wish to express my sincere thanks to 

 Dr. Harris H. Wilder and Dr. B. F. Kingsbury, who have kindly pre- 

 served and sent to me all my Spelerpes material. 



B. Methods. 



Several methods of preservation and staining were tried, but the mate- 

 rial preserved in four per cent formalin and stained with Heidenhain's 

 iron haematoxylin was the most satisfactory. The decolorizing process 

 was stopped at the moment when the other tissues had given up their 

 stain but the nerves still retained the deep blue color imparted to them 

 by the haematoxylin. It was in this way that the series which served 

 for the reconstructions were made. The sections were cut parallel to the 

 sagittal plane through the left half of the head of a larva 23 mm. long, 

 and were 20 fx thick. Figures 1 and 3, representing the nerves of the 

 left side as projected on the sagittal plane, were made by outlining the 

 accurately superposed images of the successive sections given by an Abbe 

 camera. To insure the proper superposition, direction planes were em- 

 ployed. Before sectioning, the paraffine block was cut in prismatic form, 

 the bounding planes being perpendicular to the prospective plane of 

 sectioning ; the faces of the prism were painted with a mixture of lamp- 

 black and turpentine ; the block was then quickly immersed in rather soft 

 paraffine and again trimmed before sectioning. The rim of black around 

 each section afforded a satisfactory means of accurate superposition. 



Figures 2 and 4, representing projections on the frontal plane, were 

 constructed from the same series, by plotting on millimetre paper the 

 positions of the nerves as they occurred in the successive sections. 



