OLFACTORY CELLS. 209 



the extremities of the olfactory cells (fig. 342). The rela- 

 tions just described are found to occur with very unimportant 

 modifications in all animals, and even amongst the Invertebrata, 

 as in the Cephalopoda (Sernoff). 



Max Schultze, however, states that in Man, as well as in 

 Mammals generally, the olfactory cells have no cilia, or, as he 

 terms it, no olfactory hairs ; in other words, he maintains that 

 these hairs form no necessary conditionfor the perception of smell, 

 and therefore are not deserving of any special name. When the 

 olfactory hairs are present (as in Birds and Amphibia), they 

 appear either in the form of stiff hairs, of which only one is 

 supported by each cell, or of a bundle of fine cilia. In some 

 few animals olfactory cells occur possessing both kinds of hairs. 

 Occasionally that portion of the olfactory cell where the nu- 

 cleus lies is fusiform. In some animals the external processes 



Fig. 342. 



Fig. 342. Surface view of the epithelial layer of the olfactory 

 region, after treatment with nitrate of silver. From the Proteus. 



are remarkably thick, in others they are delicate, and become 

 varicose under the influence of macerating fluids. Max 

 Schultze has further demonstrated that the large epithelial 

 cells are, in many Mammals, more or less strongly pigmented, 

 the yellow pigment lying either near the outer surface or 

 nearer their centre, and that to the presence of this pigment 

 the above-mentioned tint of the olfactory region is due. 

 Both in Man and Mammals generally, epithelium, free from 

 olfactory hairs, occurs in this region ; and although in the 

 former ordinary ciliated epithelium occurs here and there, no 

 true olfactory cells can be found interspersed amongst the others. 

 In the Plagiostomata, on the contrary, the parts capable of per- 

 ceiving odours are especially covered with ciliated epithelium. 



Besides the two kinds of cells just described, another kind 

 exists in the Plagiostomata (Max Schultze), in the Proteus and 

 Triton (Babuchin), and perhaps also in many other animals, 



VOL. in. p 



