INTERMUSCULAR NERVE CELLS OF EARTHWORM 159 



and reduced in a 1 per cent solution of hydroquinone for twenty- 

 four hours. Following routine procedure, the tissue was sectioned 

 and mounted in balsam, with cover-glasses. Preparations left 

 uncovered were found to deteriorate very rapidly. The pjTidine- 

 silver method of Ranson, and Ramon y Cajal's technique un- 

 modified were also tried, but did not yield so uniform and excel- 

 lent results as the method just outlined. 



Both the methylene-blue stain and Ram6n 3^ Cajal's modified 

 silver-nitrate impregnation left the intermuscular cells clearly 

 outlined, although the pictures presented differed greatly. The 

 silver method showed only neurofibrils and left the cell body and 

 nucleus practically colorless, while successful methylene-blue 

 stains colored the entire cell. Since the silver-nitrate method 

 was known to be uniform in its action, it was chiefly relied upon 

 in the determination of the number of nerve cells present in the 

 different regions. Methylene blue, while capricious and dis- 

 couraging to work with, proved very useful in the tracing of cell 

 processes and in the determination of their relations to other 

 cells and tissues. 



THE INTERMUSCULAR NERVE CELLS 



All preparations showed both bipolar and tripolar cells, but the 

 number of bipolar cells was greatly in excess of the number of 

 tripolar, the proportion being approximately 5 to 1. The cells 

 did not exhibit any very definite or regular arrangement, but 

 were usually scattered irregularly along the nerve rings. There 

 was, however, in many cases a marked tendency toward grouping 

 in the intersetal tracts. 



The number of cells found in the three nerve rings varied 

 considerably. The largest numbers were invariably found in the 

 posterior rings, and the highest record for this location was fif- 

 teen, eleven bipolar and four tripolar cells. Next in order came 

 the anterior nerve ring with an average of six cells, while the 

 middle ring usually contained very few cells, five being the maxi- 

 mum observed. 



