Jacobsons Organ and the Eespiratory Mechanism 



of Ainphibians. 



H. L. Bruner, Ph. D., 



Professor of Zoology, Butler College. 



Because of the fact that different parts of the nasal cavity have 

 different relations to the respiratory currents, Seydel (1895) and 

 his followers have recognized, in the nasal organ of higher amphi- 

 bians, two functionally more or less distinct parts: a true olfactory 

 cavity which is used primarily for testing the inspiratory currents, 

 and an organ of Jacobson which receives its Stimuli chiefly through 

 the medium of the expiratory current. These two cavities are also 

 more or less distinct morphologically. The organ of Jacobson is a 

 blind sack or groove which opens into the true olfactory cavity, 

 from which it is separated by a certain amount of indifferent epi- 

 thelium, the so-called respiratory region. 



In Necturus and Proteus a true organ of Jacobson is wanting 

 (Seydel, 1895; Zuckerkandl, 1910; Anton 1911) and the olfactory 

 cavity presents a very simple condition. Seydel and Anton regard 

 this condition as a primitive one, but recent observations made by 

 me on the respiratory mechanism of the lower urodeles (Bruner, 

 1913) show the possibility of another Interpretation in harmony with 

 the view that Necturus and Proteus are permanent, more or less 

 modified larvae. According to this Interpretation the simple olfactory 

 conditions are due to degeneration caused by the persistence of a 

 larval respiratory mechanism. It is the purpose of this paper to 

 present the evidence in favor of this view 1 . 





1 A short paper on this subject was read at the Cleveland meeting of the 

 American Society of Zoologists, Dec. 30, 1912. (Abstractin Science, Vol. XXXVII' 

 1913. p. 267.) 



