44 JOURNAL OF Comparative Neurology. 



cept in the case of perfectly preserved material, to follow the 

 nerve fibers to the bases of the cells of the higher series, i, e., 

 those about the sides and ectad of the Leydig cells. In good 

 methylene blue specimens stained inU-a vitain (Figs. 21-23), the 

 fibers can be traced for a considerable distance into the epithe- 

 lial layer among the intercallary nuclei, but it is only in speci- 

 mens stained with picrocarmine and haematoxylin that the ac- 

 tual connection with the cells can be made out. Even here the 

 question (always left wholly undecided by the methylene blue 

 method) as to the nature of the association is not entirely de- 

 prived of its ambiguity. When a fiber of naked nerve-plasm 

 unites with a protoblast of naked cytoplasm, who shall say 

 whether the connection is primary or secondary in the absence 

 of the most intimate embryological evidence or regeneration ex- 

 periments ? 



An important question in this connection is that as to the 

 source of the nerve fibers. Do they arise in the prota of the 

 skin or do they enter the skin from out-growths of the spinal 

 ganglia ? It would seem natural to conclude that the latter is 

 the case, and yet it is not a little puzzling to see that nearly 

 every cell in this series has its fiber. Then, too, the fact has 

 been repeatedly observed that the protoblasts are continually 

 dividing, even in rather large specimens of axolotl. (Fig. 20). 

 It must be left to careful embryological studies to decide wheth- 

 er there are cells of origin in the skin for centripetal nerves or 

 not. Another question must await either an embryological or 

 pathological solution, and that is the detection of centrifugal 

 fibers among those entering the skin. Such non-medullated 

 fibers doubtless occur and we may think of the plexus immedi- 

 ately below the epithelium is the probable site. 



We have sought to verify the results above described by 

 the application of the methylene blue intra vitain method as 

 well as the tissue methods used by Dogiel, Bethe and Huber. 

 Making all due allowance for the ambiguity of these methods, 

 it seems that the results are in harmony with those above men- 

 tioned. It is not difficult to secure impregnations in which 

 every fiber is stained throughout its course through the corium, 



