THE NASAL ORGANS OF PIPA AMERICANA. 105 



In Rana esculenta, as described by Seydel, the cuvum 

 nasale and the nasal canal are not diflferentiated from each 

 other, and, while the cavum nasale terminates in both in 

 a cul-de-sac, this termination in Rana is in front of the 

 external nares, in Pipa behind it. Then, too, the lateral 

 nasal canal of Pipa is a structure differing considerably 

 from that of Rana both in position and in histological 

 differentiation. In Rana, Jacobson's organ lies beneath 

 the main nasal canal (cavum nasale) and extends inwards 

 as far as does any other structure connected with the 

 olfactory region. In Pipa, on the other hand, it is not 

 covered by any of the other nasal structures, and it is 

 placed entirely on the external side of the whole nasal 

 apparatus. From the whole course of the duct, so far as 

 developed, the naso-lachrymal canal in Pipa will appar- 

 ently connect with the cavum nasale, while in Rana it 

 opens into the lateral nasal canal. The most posterior 

 blindsac, given off behind Jacobson's organ, is apparently 

 unrepresented in other Amphibians so far as I have 

 studied the literature. Its lack of specialized sensory 

 epithelium would seem to imply that it was of no great 

 importance. 



It seems uimecessary to make any comparisons with the 

 Urodeles farther than to point out that in some respects 

 Pipa seems to be intermediate between these and the 

 Anura, especially in the relationships of what I have 

 called the nasal canal, which agrees well in some respects 

 Avith what Seydel calls the respiratory duct. Again the 

 position of Jacobson's organ is nearer that found in Uro- 

 deles than that occurring in Rana and Pelobates. 



Comparisons with the account given by Born ('77) 

 of the conditions found in Pelobates show differences as 

 great as those occurring between Pipa and Rana. One 

 thing that is necessary in these studies is a new nomen- 

 clature of the parts. The terminology employed by 



