Olfactory Rccictioiis ni Fishes 537 



I, therefore, took this phase of their activity as the one to be tested 

 in connection with their olfactory apparatus. 



A number of fishes that had been without food for several days 

 were isolated in small vessels of water and, after an hour or more, 

 when they had come to rest, they were tested with a solution 

 filtered from a mixture of freshly chopped earthworms and tap- 

 water. By means of a very fine glass pipette a small amount of 

 this solution was discharged directly over the anterior olfactor 

 aperture of a given fish and the fish was then closely watched. 

 Notwithstanding the most careful manipulation, more or less of 

 this solution could be seen at times to be swept into the mouth 

 of the fish by the respiratory current and may well have stimu- 

 lated the gustatory organs in that cavity. The subsequent move- 

 ments of the fish were extremely irregular, and, though I was 

 reasonably sure that as a result of the application of the solution 

 the fishes respired more deeply and fully than before, I could not 

 be certain that this reaction was not due to oral stimulation. 

 Though I could see that some of the solution applied to the nasal 

 aperture was sucked into the mouth, I was unable to make out 

 whether any of it really entered the nasal chamber itself. As it 

 is essential for the stimulation of the olfactory surfaces that the 

 exciting material shall make its way to them, I turned next to the 

 accessibility of these surfaces from the exterior. 



The nasal apertures of the catfish are apparently always open 

 and when a fish is swimming with some vigor through the water 

 its motion doubtless drives a current of water through each nasal 

 chamber. I tried to demonstrate this current indirectly by mak- 

 ing a fish swim for five minutes through water containing a small 

 amount of starch in suspension and then comparing the con- 

 tents of its nasal chambers with that from the chambers of a fish 

 that had been held motionless for a like period of time in the same 

 water. So far as the comparison was concerned, the results were 

 inconclusive, but the microscopic examination of the freshly 

 opened nasal chambers led to the discovery that they were lined 

 with cilia which were beating vigorously and persistently. 



To ascertain whether these cilia produced a current of water 

 through the nasal chambers, a freshly prepared fish-head was 



