142 Journal of Comparative Neurology 



The Sarasin brothers have some time since suggested that 

 a diverticle of the nasal cavity of the salamander larva and newt 

 may be homologous with this so-called Jacobson's organ of 

 Gymnophiona, but no researches had yet been made. Burck- 

 hardt suggests that possibly the salamander is derived from 

 forms which originally possessed a Jacobson's organ. We think 

 it more likely that the salamander is a transition stage, as above 

 suggested, in which the diverticle, which is the fundment or 

 proton of Jacobson's organ, is not yet separated to act as a dis- 

 tinct organ. 



Figs. 3 and 4, Plate XII, represent dorsal and ventral views 

 of the model of the right nasal cavity of the American salaman- 

 der, Amblystoma punctalmn. Contrary to the general configura- 

 tion of the nasal cavity of the frog, tadpole, etc., the curvature 

 presents its convex surface toward the median line, or vice 

 versa, its concave aspect is laterad. This peculiarity of curva- 

 ture is constant among salamanders : see the model of European 

 Salamandra atra, Figs. 1 and 2, Plate XI, drawings, etc. This 

 curvature brings the external and internal nares toward the lat- 

 eral line, whereas in the tadpole the internal nares are further 

 toward the median line. The relative position of the nares in 

 the adult frog or tree-toad is more nearly comparable to the con- 

 dition in Salamandra both larval and adult. In following 

 through a series of transverse sections of the nasal cavity of this 

 type, we find the diverticle, which we attempt to homologize 

 with the Jacobson's organ of higher types, lying quite laterad: 

 see Figs. 3 and 4, Plate XII, jd; and Figs. 8, 9, 10, Plate V. 



In Salamandra atra this diverticle lies more ventrad : see 

 Fig. 2, Plate XI, Jd; while in larval Anura it lies on the ven- 

 tral median aspect: see Figs. 7 and 8, Plate XI, jd; and Fig. 

 5, Plate XI, id. In adult Anura it seems to become partly ob- 

 scured by the change in external configuration; — the crowding 

 forward and shortening of the longitudinal axis of the whole 

 cavity. But even there it remains discoverable in the light of 

 this homology, being confused by some authors with the so- 

 called maxillary sinus which does not occur in its true form in 

 the amphibian nasal apparatus. 



