Jelliffe, Cytology of the Brains of Some Amphibians. 147 



in the central nervous system of vertebrates, especially the mo- 

 tor cells in the ventral columns of the cord and those in the 

 nuclei of origin of motor nerves, possess a characteristic struc- 

 ture in the presence of what has been termed the chromophilic 

 granules. In general these granules may be described as elon- 

 gated rod-like, tetrahedronal or irregular portions of protoplasm 

 apparently situated in all parts of the cytoplasm, including the 

 dendrites. In the majority of the cases they seem to occupy 

 the periphery of the cell (cytoplasm) and appear to be arranged 

 in no definite way save perhaps somewhat elongated in the di- 

 rection of a contiguous dendrite or circularly about the nucleus. 



These granules possess marked chemical affinities for cer- 

 tain dyes of the indo-phenol series, notably, methylene, thio- 

 nine and toluiden blue, though they can be demonstrated by a 

 number of coloring agents. A great variety in the number, 

 shape, size and arrangement has already been described and it 

 becomes a matter of importance to arrive at some definite con- 

 ceptions regarding them or the cells in which they are found. 



The phylogenetic mode of approach has seemed the one 

 which might give the truest answer to this question and the 

 brains of the Amphibia have first been chosen for study. Meno- 

 poma, Diemyctylus and Rana have been studied casually, but 

 Necturus was chosen as the basis of the following outline. 



If this animal represents a retrograde form in a permanent 

 larval condition, it should give pictures of extreme simplicity 

 and the origins of some of the higher types of nerve cells might 

 be here found. 



METHODS. 



It may be a matter of tedious annoyance to have to detail 

 the methods by which any results have been attained, yet such 

 is the great amount of technical refinement that it is necessary. 



Several preliminary experiments were made with the view 

 of determining the action of different fixing agents. These ex- 

 periments were first made upon the cord of Necturus, but as 

 this was so small the cord of the cat was finally chosen. Imme- 

 diately after death the cord was laid bare and a small piece 



