Herrick-Coghill, Nerve Endings in the Skijt. 35 



apparently from the_ trigeminus, terminate in free arborizations 

 between the epithelium cells. A very large following of the 

 new school are prepared to claim that the conditions in the ol- 

 factory epithelium are peculiar to it alone and it is even at- 

 tempted to correlate this with a supposed fundamental differ- 

 ence in origin and structure of the olfactory from all other 

 nerves of the body. But we are able to show that in the epi- 

 dermal sense buds of the tree frog and other amphibia the same 

 continuity of nerve fiber and cell can be determined. 



It has not been an altogether unnatural result of the re- 

 markable complications of nervous structure revealed by the 

 so-called specific methods that the results obtained by the old 

 histological methods have been discredited and it has required 

 some year's experience to teach us the danger of too explicit 

 reliance on the former. Perhaps the greatest of these 

 sources of ambiguity arises simply from the fact that has been 

 regarded as the chief excellence of these methods, namely that 

 the selection is so perfect that other tissues than those selected 

 not shown at all or, even if the after-staining of sections suc- 

 ceeds, the conditions of impregnation are so unlike that the 

 tracing of connections or definite relations is difificult or impos- 

 sible. The absolutely contrary results of Dogiel and Cajal in 

 the matter of the anastomoses in the retina illustrate the diffi- 

 culty that exists even where the methods used are similar. The 

 results of our own studies are rather to confirm many of the 

 old observations and to show that there are two distinct classes 

 of dermal endings. Of these the olfactory illustrates one and 

 the most primitive one. In this case we have to deal with the 

 remnants of nervous aggregates which were originally formed 

 in or near the outer layer and in the phylogenetic development 

 have not been diverted to a deeper level as is true in so many 

 other instances. 



In our laboratory in 189 1 we made out the fact that in 

 the oral region of the earth-worm there are cells in the 

 skin which have a nervous nature and whose processes pass 

 en tad to the central system. Owing to a delay in the other 

 aspects of the research the observation w^as not made public till 



