(384 Dr. HARRIS H. WILDER. 



sides, but unlike the case of Siredon, is entirely distinct from them. 

 This septum possesses on either side a posterior lateral process, which 

 is imbedded in the substance of the ethmoid, in the same manner as 

 are the posterior processes of the nasal capsule. 



B, Cavity of the nose. 



The nasal cavity of Siren shows an exceedingly complex structure, 

 being in that respect very unlike that of the other Perennibranchs, 

 and reminding one of the complex cavity of the Gt/mnophonia. The 

 relations of these parts are best shown by a series of cross-sections 

 through this region, the most essential of which I have figured in 

 fig. 12 A, B, C. 



Commencing at the posterior end of the cavity, the posterior nares 

 open almost directly upward into a large oval posterior chamber, 

 a little flattened from above downwards. From the walls of this 

 chamber, a series of radial partitions extend inwards towards the 

 centre, between which smell-buds are situated (fig. 12 A). 



These partitions, composed of connective tissue, are thin, and bear 

 at their edges several rather crowded rows of columnar epithelium 

 which serves to protect the sensory cells of the smell- buds. A section 

 taken a little farther forward (fig. 12 H) shows a gradually exten- 

 ding shelf or partition which originates at the lateral inferior angle 

 of the cavity and anteriorly extends more and more upwards and in- 

 wards towards the opposite side, until it has effected a complete sepa- 

 ration of the cavity into a principal superioi-, and an accessory inferior 

 cavity. Of these the inferior, which is the smaller, extends a little 

 farther forward, forks and ends blindly in a sort of double sack. 

 A section taken in the region of this last division shows three nasal 

 cavities, distinct from one another (fig. 12 C). The superior chamber, 

 which is the principal cavity, continues forward, and at the anterior 

 end, communicates with the exterior by the external nasal opening. 



In the general figure of the nasal region, I have indicated by 

 transverse lines the regions from which the several sections (fig. 12 A, B, C) 

 were taken. 



I will take occasion to mention here several interesting points 

 described by former investigators, which are necessary for the com- 

 plete description of the nasal cavity. Fischer (J. 114) describes 

 a system of three valves situated at the internal nares, which serve 

 to direct the stream of water backwards. 



