1909.] OLFACTORY ORGAN OF TELEOSTEAN FISHES, 627 



So far as could be seen the passage of water through the nose 

 is quite independent of the movements of the bones of the skull 

 and is probably due to the action of cilia, though this leaves 

 unexplained the use or meaning of the vacant prolongation of the 

 nasal cavity and the valvular borders of the posterior nostril. 



The rosette is similar in form to that of Clarias bvit the laminae 

 have well pronounced linguiform processes. 



Gymnotid^. 



Gymnotus electricus. 



The nostrils lie towards the point of the snout upon the upper 

 surface of the face, the anterior at some distance (rather more than 

 the diameter of the eye) in front of and below the posterior. Both 

 are small round apertures, the posterior flush with the surface, the 

 anterior with a swollen border scarcely prominent enough to be 

 called a tube. 



The olfactory chamber is a simple flattened cavity of oval or 

 diamond shape in surface view and so placed that its short axis 

 forms the line connecting the nostrils. It is completely filled by 

 a rosette of some 20 claw-shaped laminte arranged around a central 

 axis, and lies directly upon the jDremaxilla in such a position that 

 its walls could be little if at all afiected by the movements of the 

 neighbouring bones of the skull. 



Summary. 



In the Ostariophysi examined the olfactory organ of the Carps 

 is entirely difl^erent from that of the Siluroids. 



In the Carps the organ is of a simple character and very 

 constant in structure so far as observed, differing only in un- 

 important details. In no instance were there sacs accessory to 

 the olfactory chamber, and when there was any mechanism for the 

 jjroduction of water currents in the nose it had the form of a flap 

 of skin standing up behind the anterior nostril to deflect water 

 into it in forward progression. 



The Siluridpe on the other hand show a distinct leaning towards 

 the Eels in the structure of the olfactory organ. The anterior 

 nostril tends to be strongly tubular and the jDOsterior is frequently 

 valved. The rosette is more or less elongated and consists of a 

 relatively large number of parallel laminae. 



A tendency is also observable in this family towards the 

 development of an accessory sac in extension of the true olfactory 

 chamber which in some instances by movements of certain bones 

 of the face can be contracted and expanded, thus giving rise to 

 water-currents within the nasal cavity. 



In the Gymnotidfe the olfactoiy organ, although peculiar, more 

 nearly resembles that of Siluroids and Eels than that of the 

 Carps. 



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