94 Journal of Comparative Neurology. 



the ending of the fibres of Miiller, any more clearly than Ahl- 

 born could with the carmin method. I tried to combine the 

 Golgi and the carmin methods, with no better results. The 

 fibres stained very clearly, the cells how ever remained un- 

 stained. The fresh material at my disposal was so limited 

 that no modifications of the methods could be tried. 



The transverse fibres which Retzius stained in Myine glu- 

 tinosa with methyl blue, were not at all impregnated in my 

 preparations. 



The glia cells are found quite frequently in the grey and in 

 the white matter. They possess a small cell body, with granular 

 protoplasm and a corona of fine processes going off from every 

 side. Their size varies very much. I mistrust that many of 

 them were interpreted as nerve cells by Reissner and Ahlborn. 



These authors made three {Reissner) and four {Ahlborn) lay- 

 ers of proper nerve cells and find them most numerous about 

 the central canal and in the lateral parts just where the glia cells 

 above described are also found. I would suggest that these 

 cells may be looked upon as undifferentiated intermediate ones, 

 between the glia and fully developed nerve cells. 



The processes of these " arachnoidal cells " end in small 

 nodules, passing upward and downward to the periphery of the 

 spinal cord, also uniting both surfaces together, a relation which 

 is not found in any other vertebrate, so far as I know. 



TLATE XIV. 



In the figures I combined the most characteristic features from sev- 

 eral preparations, but tried, however, not to embrace more in one draw- 

 ing than is usually seen in a good preparation. 



Fig. I. Transverse section of Petromyzon fiuv. medulla. 



pc. Posterior cells of Freud, (remain unimpregnated;) gc. Ganglion 

 cell; cc. Commissural cell; Mull. T. Tubes of the Mullerian fibres, some 

 of them containing the fibres; Glc. Glia cells, the two layers. 



Fig. 2. Dorsal view of an impregnated and cleared segment of 

 spinal cord. 



d. n. r. Entering dorsal nerve rod, showing T and Y branching 

 fibres; Ahi/l. f. Mullerian fibres, straight course; itnd. f.f. Undulating 

 fine fibres withcol lateral branches. 



Fig. 3- Typical ganglion cell with three protoplasmic processes. 



