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THE A M ERIC AN NA TURALIST [Vol. XXXV 1 1 . 



the operation I attribute to the increased use of the eye as an 

 organ for orientation and though this is an assumption on my 

 part, it is one well supported by evidence from the invertebrates, 

 and, until it is shown to be false for fishes, it seems to me to 

 make Professor Tullberg's conclusion that the fish ear has noth- 

 ing to do with equilibration at least premature. 



My observations on the lateral line organs ol hunduius 

 (Parker, 1903, pp. 59-62) are in entire agreement with those of 

 Professor Tullberg (1903, pp. 8, 15) on these organs in other 

 fishes in that I have found no evidence that these organs are 

 essential to the normal swimming of a fish against a current. 

 But since in Fundulus I could not persuade myself that the ear 

 was not in some degree connected with equilibration, I was 

 unable to devise a satisfactory experiment that would test in the 

 absence of the ear, other organs of sense, such as the skin, that 

 might be stimulated by water-currents. The only evidence I 

 was able to obtain was that when fishes whose spinal cords and 

 lateral-line nerves had been cut several days before, were held by 

 the head near a gentle current of water the tails bent toward 

 the current even though the ac tion of the current on a cordless 

 fish similarly held was to force the tail in the opposite direction. 

 I am, therefore, entirely certain that the skin of the trunk of 

 l-'unditlus he tt roc lit us is stimulated by water-currents, though 

 I cannot say that these may not also stimulate the ears. I must 

 confess, however, that Professor Tullberg's evidence (1903, pp. 

 11, 14,) on this point, namely, that after cutting both horizontal 

 semicircular canals the fish no longer orients to a current, does 

 not seem to me wholly conclusive, for this operation may bring 

 about the observed condition by a slight interference with the 

 eq 1 1 1 ti 1 function of the ear. In Fundulus swimming against 



as equilibration organs ,and, secondly, directive locomotion which 

 is dependent upon the stimulating effect of the current on the 

 skin of the fish. Under these conditions an interference with 

 the ear might well give rise to a loss of rheotaxis though the 

 primary stimulus for this form of response might be received by 



