ANATOMY OF THE OLFACTORY ORGAN 33 



Grassi and Castronovo (1889) in the dog, and subsequently 



was identified by Alcock (1910) in the pig. In this mammal 



the epithelium of the intermediate zone is thicker than that 



of the respiratory region and thinner than that of the 



olfactory region. Besides basal cells it possesses two 



types of epithelial cells, ciliated cells like 



those of the respiratory epithelium and 1 



non-ciliated sustentacular cells like those 



of the olfactory region. It also contains 



many olfactory cells, but these cells are 



not as numerous in the intermediate zone 



as they are in the olfactory region 



where they are said to make up about 



seventy per cent of the cells present. It 



is plain from the accounts given that 



the intermediate zone is a region of 



transition between the two chief nasal FIQ.Q 



preparation of an 



regions, the olfactory and the respiratory. a lf pike ry (E e sox) ro in 

 5. Polymorphic Cells. In most verte- Srb.3? ffl 



brates the olfactory cells exhibit great process ne arl" 



. ,, . . ,, -.- ., , shown, but also the 



umtormity 01 structure. In the fishes, ion g peripheral oi- 



factory flagellum. 



however, Dogiel (1887) has called attention 

 to a polymorphism among these elements, 

 and he has described in addition to the ordinary type of 

 spindle-shaped olfactory cell, cylindrical olfactory 

 cells and conical olfactory cells. These three types 

 have been identified by Morrill (1898) and by Asai 

 (1913) in a selachian (Mustelus) and by Jagodowski 

 (1901) in the pike (Esox). To what extent this 

 polymorphism occurs in other vertebrates and how 

 important it is for a right understanding of the action 

 of the olfactory organ has not yet been determined. 



3 



