io Journal of Comparative Neurology. 



parallel to it until the points of least resistance are found, that 

 they then penetrate and send non-medullated nerve-fibres among 

 the epidermal cells, where they branch freely but in no case 

 penetrate within the cell walls (Figs. I, 2, 5.) 



Kolliker in his "Histologische Studien an Batrachier 

 Larven " x thinks that at first the nerves are non-medullated and 

 are in the form of pale anastomosing branched fibres. Even at 

 this early stage they are composed of a central fibre, or axis- 

 cylinder, and a sheath. In the earliest stages he agrees with 

 Hensen in saying that these fibres are without nuclei. As the 

 nuclei are absent when the nerves emerge from the cord, they 

 must either arise in loco or apply themselves to the fibres from 

 some other source. He notices that the intervals between 

 nuclei are greater in earlier than in later stages, that the nuclei 

 multiply by mitosis, and he is inclined to the view that they are 

 applied to the exterior of the sheath from without. As to the 

 nature of the peculiar skein-like bodies in the cells he is unde- 

 cided ; he notices, however, that they rarely, if ever, reach cell- 

 walls. He thinks that they are not nerves and says that their 

 function and chemical composition are unknown. Mitrophanow 

 also finally decides against the nervous nature of these thread- 

 like bodies and says that the nerves end free among the epider- 

 mal cells. 



Most of the sections which we have examined were pre- 

 pared by the paraffine method after hardening in dilute chrom- 

 acetic for 24 hours. Some were stained with aqueous haema- 

 toxylin, some with haematoxylin and picrocarmine, others with 

 haematoxylin and acid fuchsin. The latter served especially 

 well to differentiate the nerve fibres from the intra-cellular skeins. 



DESCRIPTION OF PLATE I. 

 Sections through the skin of the tadpole of the frog at different ag«s, all 

 taken shortly before the metamorphosis, between the appearance of the hind 

 legs and that of the front legs. 



1 Zeitschrift filr wissenschaftliche Zoologie, XLIII, I, 1886. 



