144 Journal of Comparative Neurology 



terminus is with its concavity mesad. In the proximity of the 

 internal opening it is characterized by a great thickening of the 

 epithelial wall (Fig. 3, Plate X, t). On the outer aspect of the 

 cavity among the rather irregular modifications of the epithe- 

 lium wall, an outer small diverticle is apparent which is quite 

 distinct from the mere corrugations of its surface. See od, Figs. 

 1, 2, Plate VIII, 2 and 5, Plate X, and Fig. 6, Plate XI. This 

 diverticle is evidently transitory as it does not appear in either 

 of the older specimens (Figs. 6 and 7, Plate X, and Figs. 7, 8, 

 Plate XI). On the inner aspect midway between the nares, 

 rather ventral than dorsal, and somewhat lower and further for- 

 ward than the smaller outer diverticle, is situated another and 

 larger diverticle which, as has been hinted, may be homologized 

 with Jacobson's organ in higher types (Reptilia etc.) See Figs. 

 2 > 3> $> 6, 7, Plate X, and Figs. 5, 6, 7, 8, Plate XI, id and jd. 

 Large and apparently active glands lie immediately dorsad and 

 in close connection with the diverticle, having also close con- 

 nection with the general cavity, in the epithelial interspaces. 

 See Figs. 6, 7, Plate X, Figs. 6, 7, Plate XI, gla, epi. 



Fig. 6, Plate X, represents the inner aspect of a model of 

 an older tadpole, over a centimeter in length, of the same 

 species ;jd represents in this figure the inner larger diverticle 

 homologous, as we believe, with Jacobson's organ in Reptilia. 

 Fig. 7, Plate X, shows a view of the same model looking down 

 from above as it would be situated in its place within the right 

 side of the head of the tadpole. The marked difference be- 

 tween the model figured in Fig. 5, Plate X, and Fig. 6, Plate 

 XI, and this one, lies in the disappearance of the outer smaller 

 diverticle, and in the comparative enlargement of this inner 

 larger one with its glands (Figs. 6 and 7, Plate X, gld). The dif- 

 ference in the absolute size of the models, as in the other cases 

 is due partly to the fact that lenses of different degrees of mag- 

 nification were used to make the camera drawings in the different 

 cases, and partly to the real differences in the sizes of the speci- 

 mens under investigation. 



In Fig. 1, Plate X, we have a camera sketch of a horizontal 

 section through the right cavity of the tadpole modelled in Fig. 



