662 ON THE OLFACTORY ORGAN OF TELEOSTEAN FISHES. [May 25, 



The currents produced normally by these sacs are rhythmical *, 

 flowing in and out of the nose as the fish gently opens and closes 

 its mouth in breathing, and may be compared to the air-currents 

 in the Mammalian nose during oi-dinary respiration. The strength 

 of the cuirent must, however, be quite vinder the control of the 

 fish, for stidden and energetic movements of the jaws would 

 naturally prod vice corresponding sudden and strong currents in 

 the nose, comparable to a snifi". In noses of this class it is gene- 

 rally arranged by means of valves that the water shall enter by 

 the anterior nostril and leave by the posterior. 



A study of the anatomy of these parts leaves little doubt that 

 their action is somewhat as stated above, but the facts detailed by 

 Bateson from direct observation of the living fish make it difficult 

 to account for the presence of these dili'erent and often elaborate 

 mechanical devices. He states, and his experiments are quite 

 conckasive, that practically all Teleostei seek their food by sight, 

 and apparently have no appreciation whatever of what we term 

 smells, so that it still remains an open question what their olfactory 

 organ is sensitive to, and what part in their economy it fills. 



Apart fi'om the essential structural identity of the fish olfactoiy 

 organ with that of higher Vertebrates, the mechanisms by which 

 the surrounding medium is brought to play upon their sensitive 

 membranes gently or violently at will are so closely analogous that 

 one would be almost compelled to regard their functions as also 

 essentially the same, did not Bateson's observations prove beyond 

 question that the sense of smell in the ordinary sense of the word 

 is absent in the vast majority of fishes, and it is to be noticed that 

 it is just in those cases where it is absent that the mechanisms 

 for regulating the water-currents within the nose are the most 

 efficient. 



It should, on the other hand, be observed that in a large number 

 of the more highly specialized fishes there is a close connection 

 between the nasal water-currents and the respiratory movements 

 of the jaws, a fact that suggests that the nose may have more to 

 do with respiration than with the discrimination of food, and 

 possibly may be of some use in testing the water used for 

 respiration. 



The Relation betvjeen the Strihcture of the Nose and 

 General Habit. 



Although it is difficult to obtain accurate information concerning 

 the habits of sea-fishes, enough can be ascertained (Day's ' British 

 Fishes,' Cunningham's ' Marketable Fishes,' &c.) to roughly group 



* In many fishes (Bateson, I.e. p. 230) oscillating currents keeping time with the 

 movements of the jaws in respiration have been directlj' observed, but they are not 

 a necessary result of these movements, for although under normal conditions the two 

 go together, the current may stop while the respiratory movements continue. 

 Whether this depends upon a voluntary closure of the nostrils or what its explana- 

 tion may be there is at present no evidence to show. 



