Herrick-Coghill, Nerve Endings in the Skin. 37 



muscle comes in contact with a nucleus of the muscle which, 

 under the stimulus afforded, begins to proliferate and the pro- 

 toplasm of the cells so formed assumes an intermediary char- 

 acter and spreads out upon the surface of the muscular band as 

 a means of applying the stimulation. To us the first is in the 

 absence of direct evidence the more probable solution. 



Observations are at hand which tend to show that exten- 

 sive nervous proliferation takes place below the corium of the 

 skin at an early stage. In section of the skin of Amphibia these 

 proliferating cells can be seen and this is probably the origin of 

 the ganglion plexus of the skin. (Figs. 3, 5 and 6, Plate V.) 

 To pass then to the nerve endings in the skin, we may first 

 note the isolated sensory cells. These may be seen in suitably 

 prepared sections of the head in the tree frog and other Anura 

 and also in the neighborhood of the eye in the axolotl and other 

 tailed Amphibia. In the tree frog, where they most numerous, 

 these cells are grouped in threes and fours in close clustres ly- 

 ing in a special cavity passing through the entire thickness of 

 the epithelial layer. The terminal segment is a slender nucle- 

 ated cell, the nucleus being very narrow. The peripheral part 

 of the cell is a narrow rod which at the periphery bears a few 

 rigid bristles. Entally from the nucleus the cell walls are very 

 delicate but obvious and the nerve fiber within is easily disting- 

 uishable in the doubly stained specimens. The fiber is easily 

 followed to the corium layer and in many cases through it. It 

 seems too that more than one nucleus can be seen in the course 

 of the fiber before the passage through the corium. The skin 

 is at this point very thick and the presence of large glands 

 serves to separate the corium from the epithelial layer, so that 

 the course of these fibers is readily followed for a long distance. 

 In the case of certain teased preparations it was possible to iso- 

 late these fibers and study them with oil immersions and there 

 can be no doubt as to the relations here described. So far as 

 could be told, these fibers do not connect with the subepithelial 

 plexus as do the fibers of the free arborizations to be described 

 later. (Figs. 2, 12, 13, 14.) The terminal segment seems to 



