54 Journal of Comparative Neurology, 



addition; with application of Delafield's haematoxylin, Benda's 

 Sulphate of Iron Haematoxylin, and Weigert's Haematoxylin. 

 Further use has been made of methylene blue intra vitam pre- 

 parations, and the silver method has also been employed. 



The methods just mentioned show that free-ending nerve 

 cells occur in large numbers in the skin on the head of the frog, 

 that these are usually found in clusters of three or more, and 

 that these clusters tend to be grouped to such an extent that 

 they appear, in our best preparations, over a comparatively large 

 field with varied frequency, while in an adjacent area they are 

 entirely absent. For their distribution and general arrangement 

 in the surrounding parts, the best results have been obtained 

 from tissues hardened in the chrom-acetic acid and Flemming 

 solutions and stained with Weigert's Haematoxylin. (Fig. i.) 

 In this preparation numerous clusters of fibers are seen to pass 

 ectad through the corium and terminate in long rod-like cells 

 in the Malpighian layer. The continuity of the terminal cell 

 with the nerve is certain. In instances otherwise clear this point 

 is made doubtful by the presence of pigment, but such evidence 

 is now in hand that the continuity of cell with nerve must be 

 accepted. This is shown also in the methylene blue prepara- 

 tions, in which case the deeply impregnated fiber has been seen 

 to pass in a similar manner through the corium and, clearly 

 differentiated from the neighboring pigment, to continue into the 

 terminal cell, the wall of which is continuous with the sheath 

 of the fiber. (Fig. 4.) The terminal cells are clearly differ- 

 entiated from the neighboring epithelial cells. They are much 

 longer than the latter, extending through nearly the entire 

 height of the Malpighian layer, usually appearing to end just 

 short of the horny surface of the skin. Their special cavity 

 through the epithelial layer and opening on the surface which 

 has been seen in other instances is not found in the later prep- 

 arations. On the contrary, the terminal cells often diverge at 

 the base of the Malpighian layer, the epithelium cells crowding 

 in between them. This discrepancy in results may be due to 

 the difference in the methods employed in the two instances, 

 though it more likely indicates that the structure in question is 



