346 S. O. MAST 



on the sea-side was everywhere very steep, and the water be- 

 came deep rapidly. On the opposite side the incline was very 

 gradual, and the water was very shallow. 



As soon as the pool was closed the fishes began to swim about 

 rapidly in an aimless sort of way. They continued for a few 

 moments, then they came very close to the edge of the water 

 and swam several times up and down the side of the pool nearest 

 to the sea. Finally a dense aggregation formed in the outlet 

 near the dam and soon, three minutes after the outlet was closed, 

 they began to come out in the angle between the outlet and the 

 dam represented by y in figure 2. The first group that left 

 the water consisted of about twelve individuals. All of these 

 followed the ridge from y to its end, and then turned and went 

 toward the sea. Other groups soon followed behaving in a 

 similar way. Many attempted repeatedly to cross the ridge 

 at y and three actually succeeded although the ridge was fully 

 10 cm. high and the incline over it formed an angle with the 

 horizontal of more 'than 45 degrees. After passing the ridge 

 some went directly across the sand-bar and entered the sea at 

 m, but many of them got into the small pool p. All of these 

 swam directly across this pool to the bank at n. Here three 

 were seen to leave the water again, climb the relatively steep 

 bank 9 cm. high and then proceed to the sea, although this 

 pool had a free passage to the outlet through which nearly all 

 escaped. This seems to indicate that after these creatures once 

 start in a given direction toward the sea they have a strong 

 tendency to continue in this direction. 



About 25 individuals were seen to leave the tide-pool at c, 

 but all returned. A few of these reached a point nearly a meter 

 from the edge of the water before they returned but most of 

 them went only a few centimeters. Quite a number also left 

 the pool at x but all of these returned after going a very short 

 distance. 



When the pool was closed there were approximately 300 

 specimens in it. The following morning 75 dead ones were 

 found; consequently some 225 must have escaped. 



2. In all of the experiments made during the falling tide 

 behavior similar to that described above was observed. In 

 some of them, there were, however, additional points of interest. 

 A detailed description of one of these follows. 



