34 Journal of Comparative Neurology. 



In a wide range of types it has been possible to make out the 

 adult conditions which have often been correctly described. 

 Merkel in his classical work gives a figure of sensory endings 

 from a cirrus of Amphioxus that compares in every detail with 

 the specific cells of the olfactory epithelium of a reptile or am 

 phibian. (Plate III, figure lo.) Few if any of those who have 

 studied the development of the olfactory will venture to deny 

 that the " Stiftzelle " at the peripheral end of the olfactory 

 nerve is a member of the nervous series having the same 

 origin, though it is doubless conceivable that, through some 

 strange fatality, every observer has failed to notice the intrusion 

 of a foreign element at some stage of the process. (Fig. 31.) 

 If, however, we take for granted that the fiber is continuous, 

 we claim that there is an equal necessity for admitting the same 

 for other clusters of nerve endings on the surface of the body. 



Although there was for a long time considerable disagree- 

 ment as to the actual connections of the olfactory nerve fibers, 

 and the classical studies of Kolliker, Klein and Piana left the 

 matter open, it seems as though the later studies of Ehrlich, 

 Arnstein, Cajal, Gehucten, Retzius, Brunn and Lenhossek, who 

 employed the silver and methylene blue methods, were sufficient 

 to prove conclusively that the olfactory epithelium possesses 

 rod cells whose proximal end is an actual continuity with the 

 fiber of an olfactory nerve filament. The writer has frequently 

 verified this in specimens of Amphibia double stained with 

 haematoxylin and picrocarmine in which very unambiguous 

 views can be secured. A few figures from these preparations 

 were published by Mr. Bawden, then a student in the writer's 

 laboratory (Jour. Comp. Neurol. IV). Our studies in the 

 development of the olfactory nerve show that the proton of the 

 nerve is formed in or under the epithelium of the nasal area and 

 that the nerve grows by moniliform concrescence of cells which 

 arise by mitosis from this proton. From this stand-point, then, 

 it would be expected that the neurocytes of origin would be 

 found in the epithelium. In all essential respects the relations 

 in Jacobson's organ are the same as in the true nasal olfactory 

 epithelium. The accompanying figure (Plate V, Fig. 10) from 

 an article by Lenhossek (Anatom. Anzeiger, VII, 19-20.) illus- 

 tjates these conditions and also the fact that other nerve fibers, 



