CHARACTERS OF THE OLFACTORY CELLS. 



207 



enlargements, and from thence we may conclude that the ex- 

 ternal process of the olfactory cells is composed of two sub- 

 stances throughout its whole length, an external, which swells 

 up under the influence of certain reagents, and an internal 

 thread which remains unaffected. The central process of the 

 olfactory cells presents the same relations, with this difference 

 only, that it is considerably finer, and in many instances is 

 immeasurable. In Tritons I have found that the length 

 of these processes, taken together with the other portions 

 of the olfactory cells, sometimes exceeds by many times 



Fig. 341. 



Fig. 341. A, an epithelial and two olfactory cells from the point 

 of transition of the olfactory region into the ordinary mucous mem- 

 brane (from the Triton) ; B, peculiar epithelial cells faom the olfac- 

 tory mucous membrane ; a, from the Raja clavata, after Max Schultze ; 

 6, from the Proteus. 



the thickness of the epithelial layer (fig. 341). They must 

 consequently either penetrate into the subepithelial layer, or 

 run in a horizontal direction along the line of demarcation be- 

 tween it and the epithelial layer. I have actually observed the 

 latter course in the Proteus. The cells that have just been 

 described everywhere surround the above-mentioned large cells 

 that possess a large oval nucleus, and extend through the whole 

 thickness of the epithelial layer ; their external half appears to 

 be more or less cylindrical in the Triton and Proteus, is trans- 

 parent, and often distinctly striated longitudinally (fig. 340). 

 I have been able to satisfy myself that this striation is not to 



