224 



ELEMENTS OF BIOLOGY 



constituted of a single sensory cell (Fig. 151); those of taste are 

 multicellular and are termed taste buds (Fig. 152). The olfactory 

 nerve endings are localized in areas of epithelium in the nasal pas- 



OLFACTORY CELL 



EPITHELIAL CELL 



NERVE FIBER 



Fig. 151. — Olfactory nerve endings in the olfactory epithelium in the human nose. 



Diagrammatic. 



sages. In many lower vertebrates and in many mammals the areas 

 are prominently placed so that the tidal air as it enters the nares is 

 in direct contact with these sense organs. In Man, however, the 



EPITHELIAL CELL 



SUPPORTING CELL 



NERVE FIBER 



TASTE PORE 



TASTE CELL 



Fig. 152. — Diagram of a taste bud from the human mouth. 



olfactory areas are in the base of folds or crypts so that in order for 

 a stimulus to be set up, the chemical in the air must be penetrating 

 or an effort be made by sniffing. The acuteness of the sense of smell 



