lOO 



BULLETIN OF THE BUREAU OF FISHERIES. 



it would strike the end a blow that could be kept reasonably constant by a gauge to 

 mark the point at which the ball was liberated. The ball weighed about 4,300 grams 

 and was ordinarily released at such a point that it struck the end of the tank with a 

 calculated velocity of 84 cm. per second; in other words, at the moment of impact 

 with the end of the tank the ball had a momentum of about 361,200 C. G. S. units. 

 This blow produced in the tank a low booming noise which was used as the stimulus 

 for the fish. It probably affected the nerve endings of the skin, of the lateral-line 

 organs, and of the ears of the fishes that were tested. 



In experimenting with a given species of fish, five individuals were placed in the 

 tank and allowed to remain there till they were thoroughly accustomed to their sur- 

 roundings, often a matter of half a day or so. Then the current of water was shut 

 off, and shortly afterwards the stimulus was applied by allowng the ball to fall once 

 every 10 seconds against the end of the tank. This was continued for 50 blows, and 

 between blows the interior of the tank was cautiously inspected from the middle of 

 one side, and a record was made of the distribution of the five fishes by noting the number 

 in the half of the tank at whose end the blow had been struck. This form of observ-ation 

 was facilitated by marking on the white bottom of the tank a transverse line that 

 divided the area in halves and that could be used as a line of reference in deciding on 

 the distribution of the fishes. After 50 trials had been made with blows delivered at 

 one end of the tank, the ball was shifted to the cord at the other end of the tank and 

 an equ&,l number of blows was delivered at that end; the combination of the two sets 

 of records thus obtained showed whether the fishes tended to approach the sound center 

 or retreat from it. The whole operation was then repeated on five new individuals, 

 and this process was kept up until reasonably constant results were obtained. In 

 all, eight species of fishes were tested, and these fell more or less naturally into three 

 classes. 



The first consisted of those fishes that on stimulation tended to retreat from the 

 region of sound production. They are well illustrated by the tautog {Tantoga onitis), 

 whose reactions are summarized in the following table: 



Table I. — Directive Responses of Tautoga onitis to Sound. 



The grand total of occurrences in a possible 2,300 in the half of the tank nearer the 

 sound was 842, or 34 per cent. 



