1909.J 



OLFACTORY ORGAK Of TELEOSTEAN FISHES. 



633 



pivot, compressing the accessory nasal sac that rests upon its 

 posterior and inner surfaces. The jaw movements may possibly 

 also be of some little assistance in the compression of this sac, but 

 those of the gill-cover appear to be by far the more important. 



The rosette is very feeble and consists of a series of low pleats 

 i-adiating from a central boss. 



Sum')nary. 



In Esox and Scopelus the olfactory organ is quite simple with 

 open non-specialized nostrils and plain cavity. It differs in the 

 two genera chiefly in the form of the rosette, whidi in Esox is 

 circular and very poorly developed, in Sco'pelus linear and sharply 

 defined with strong though small laminae. 



In the two Cyprinodonts the organ is of a quite different and 

 more highly specialized type. The anterior nostril may be tubular, 

 the posterior is valved. The nasal cavity is complicated by the 

 presence of an accessory sac of characteristic form and position, 

 'which from its position is capable of being compressed by the 

 bones of the face. The rosette is feeble and in Orestias resembles 

 in some particulars that of the Pike. 



Catosteomi. 



f1stular11d.e. 



Fistularia. 



The nostrils are two plain oval perforations in an area of soft 

 skin situated close in front of the eye between the frontal and 

 lachrymal bones. The posterior is narrow, with its chief axis 



Text-fig. 202. 

 A/.S. R. 



Fistularia sp. 



Right olfactory organ showing relative proportions of olfactory (R.) and 

 indifferent (N.S.) areas of the nasal cavit}'. 



longitudinal, the anterior about three times as large. The bridge 

 of skin between the two is about equal in breadth to the long 

 axis of the anterior nostril. The olfactory chamber is oval but 

 very shallow. It lies upon the bones of the skull (lateral ethmoid) 

 and extends backwards some distance beyond the posterior nostril, 



