Cog HILL, Skin of the Frog. 55 



of a primitive and embryonic nature, becoming obscured in 

 older tissue. The nucleus of the terminal cell, in accordance 

 with earlier descriptions, is long and narrow, as are also those 

 which appear in the nerve in its passage through the corium. 

 Here the nerve is shown by both Flemming and chrom-acetic 

 acid preparations stained with the Delafield, Benda and Weigert 

 haematoxylins, and also by the methylene blue and silver im- 

 pregnations. (Figs. 1-6.) The Weigert being primarily a 

 sheath stain, the fibers are frequently seen with difficulty by 

 that method, and to be seen at all require an exact decoloriza- 

 tion. In special instances this process was observed under the 

 microscope and the tissue removed at the proper stage of dif- 

 ferentiation. The best results, however, for showing the struc- 

 ture of the nerve in its passage through the corium came from 

 a teased methylene blue preparation (Fig. 3). In this special 

 case the Malpighian layer was in part torn away, but the glands 

 and other structures of the skin further entad were intact, so 

 that the fiber could be traced with but one short interruption 

 from immediately beneath the Malpighian layer to near the base 

 of the corium. The sheath, also, for the greater part of this 

 distance, was clearly differentiated from the fiber. Other sim- 

 ilar fibers associated with it were tracable for a shorter distance. 



The ental destination of these fibers from the terminal 

 cells is difficult to determine with absolute certainty. However, 

 in methylene blue and silver impregnations, they are traced for 

 some distance beneath the corium and in a plane nearly parallel 

 with it (Figs. 5 and 6), while with the Weigert method they have 

 been seen to enter small bundles of fibers immediately beneath 

 the skin. (Fig. 2.) This indicates that they are branches from 

 the plexus of nerve fibers and bundles which is known to exist 

 in this region. If they are such, the innervation of the terminal 

 cells on the head, as has been demonstrated from the head of 

 the tree frog for this study especially, must be by the frontal 

 branch of the fifth nerve. 



A discussion of the nerve termini on the glands requires 

 first a reference to other structures related to them. The glands 

 in the skin of the frog, as is well known, are of two classes, 



