146 Journal of Comparative Neurology 



The amphibian Anura during embryonic life are, as we have 

 said, possessed of two diverticles, an outer upper lateral and an 

 inner lower mesal one. Says Balfour (Compar. Embryology, 

 No. 8), "a diverticle of the cephalic portion of the nasal cavity 

 of Anura (frogs) is probably a rudiment (proton) of Jacobson's 

 organ." Fleischer finds the likeness between the lower diver- 

 ticulum of Anura (embryos) to the Jacobson's organ in rep- 

 tiles and describes its subsequent probable development in the 

 following words : "In the course of further development, (after 

 the diverticulum stage), it passes further downwards and in do- 

 ing so gets turned about its axis, so that the canal by means of 

 which it was still connected with the nasal cavity comes now to 

 open into the mouth cavity." We think it probable as before 

 suggested that not only is this true, but that there has taken 

 place a previous revolution from its external (lateral) position 

 ventrad and mesad from the position which it occupies in Gym- 

 nophiona and some salamanders until it reaches the position as 

 found in tadpoles, and further that this process is carried on be- 

 yond the stage mentioned by Fleischer until the diverticle 

 comes to lie entirely mesad and as a separate organ (now known 

 as Jacobson's organ). These remarkable changes in relative 

 position are made strongly probable moreover by the corres- 

 ponding shortening of the head, seen in its progressive stages 

 corresponding to the advancing revolution of the diverticle. 

 Beard is inclined to doubt the complete homology throughout, 

 but our own researches in these various types seem to confirm 

 the suggestions of Gotte, Fleischer, Born, and Kolliker who 

 have hinted at this homology. 



A cross section through the nasal sac in an adult frog, in 

 front of the internal nares, reveals three cul-de-sacs. The first 

 is an upper wide and rounded cavity, the second a smaller lat- 

 eral sac opening into the naso-lachrymal duct, and the third a 

 lower smaller cavity communicating with the mouth by the in- 

 ternal nares and with the so-called maxillary sinus by an oblique 

 cleft. The inner nares open into the mouth from the most lat- 

 eral point of this maxillary cavity. In the higher types we find 

 that this maxillary sinus, by the elongating of the palate, opens 



