104 BULLETIN OF THE ESSEX INSTITUTE. 



external nares. Its epithelium throughout is of an undif- 

 ferentiated character. 



The cavum nasale is nearly the same size and shape 

 throughout its whole length (en, figs. 2-9). It is com- 

 posed of specialized cells, and, in its grosser features, its 

 histology is similar to that of Jacobson's organ. It has 

 fine branches of the olfactory nerve- distributed chiefly 

 to its internal part. These are in many cases too small to 

 be seen with the magnification used. At its anterior end, 

 it becomes separated from the lateral nasal canal (fig. 2) 

 and soon ends as a small blindsac. 



In fig. 5, the naso-lachrymal duct is seen. It can be 

 traced for several sections, but as yet it has not formed 

 its connection with the cavum nasale, as it apparently 

 does in a later stage. 



It is yet too early too say how much w^eight is to be 

 placed upon the varying conditions of the olfactory organ 

 in settling the vexed questions of the interrelationships of 

 the Amphibia. Too few forms have as yet been studied 

 to allow of any broader generalizations. Naturally one 

 would expect to find more points of resemblance between 

 the conditions occurring in Pipa and in Rana than between 

 Pipa and the Urodeles, but from the foregoing account it 

 will be seen that Pipa is about as widely removed in its 

 nasal structure from the one as from the other. Certainly, 

 if much weight is to be given these structures, naturalists 

 are justified in the separation of the Aglossa from the 

 other Anura.3 



In more detail, these diiferences are as follows : — 



- Fischer ('43) has figured anrt described the olfactory nerve as double in this 

 species; his figures representing the two components as arising side by side, 

 directly from the l)rain. His account has often been quoted. I find, liowever, 

 that the olfactorius arises by a single root and the nerve passes undivided 

 through the ethmoidal cartilage, and almost immediately after its emergence 

 breaks up into two superimposed branches which at once sul)divide for distri- 

 bution to tlie olfactory epithelium. 



» A study of the structures In Dactylethra would prove very interesting. 



