240 PROCEEDINGS OP THE AMERICAN ACADEMY. 



The giant cells are all unipolar. At least I have never found more 

 than one nerve process, and I do not believe that more than one exists. 

 In entering the fibre of Leydig the cell-process almost always takes a 

 backward direction. Its course from the cell may be for some distance 

 forward, but before entering the fibre of Leydig it is usually found to turn 

 caudad (Plate 4, Fig. 23). In a very few instances, in tlie posterior 

 segments of Axiothea torquata, it has been seen to be directed cephalad 

 as it entered the fibre. 



The giant cells and their processes are surrounded by the same sort 

 of a sheath as that which has been described for Leydig's fibre. It is 

 evidently one continuous sheath extending around cell, cell-process, and 

 Leydig's fibre. Around the cells it shows itself to be composed of several 

 strands or lamelliE. The process from the giant cell shows an internal 

 structure identical with that of Leydig's fibre, so that the account of the 

 internal structure of the Leydig's fibre already given can be applied with- 

 out change to the individual cell-processes. In sections which show the 

 union of cell-process and Leydig's fibre there is, so far as the appearance 

 of the contents of both go, no mark by which one could be distinguished 

 from the other. Sections prepared from material treated with the vom 

 Rath mixture show a delicate gray finely granular protoplasm which 

 entirely fills the sheath (Plate 2, Figs. 15 and 16) like that which has 

 been described for the Leydig's fibre. 



b. Technique. 



The internal structure of the cell itself shows peculiar conditions, 

 which are constant and equally well shown by two entirely different 

 methods of fixation and staining; viz. (1) the vom Rath mixture already 

 described, followed by wood vinegar, and (2) a cold saturated aqueous 

 solution of corrosive sublimate followed by iron hematoxylin as a stain. 

 The first method was in some respects the more satisfactory, since it 

 seldom showed any shrinkage of the cell contents. But the iron-ha^ma- 

 toxylin stain employed upon sections fixed with corrosive sublimate could 

 be controlled more easily than the vom Rath preparations. The prin- 

 cipal results regarding the internal structure of the cell obtained by 

 one method were, however, fully confirmed by the other. It was very 

 important in the use of the vom Rath mixture that there should not be 

 too much osmic acid in the solution, and also that the material, after 

 being treated with the wood vinegar, should remain for several days, or 

 better weeks, in strong alcohol. 



