34 University of California Publications in Zoology [Vol.19 



or more often a tube 50 by 3 centimeters. The animals are very strongly 

 positive at room temperatures (lines 1 and 2), and this behavior is 

 not altered by changing the salinity. In a good many instances the 

 specimens swim down for at least a portion of the distance and swim- 

 ming often alternates with dropping. 



A comparison of the figures indicating movement in the first two 

 lines with the last two shows that at the lower temperatures there is a 

 considerable decrease in the percentages in the positive column and an 

 increase in the negative column. In other words, the animals move 

 toward the light more often when the temperature is low even if it 

 involves overcoming gravitation. Such a change in behavior is not 

 shown in tables 6 and 7, so it is to be presumed that the upward move- 

 ment shown in table 8 is a reaction to light rather than to gravity. 

 That is, the animals become positive to a vertical light as well as to a 

 horizontal one, providing the water is of a sufficiently low temperature. 

 It is interesting to note that when the lower two-fifths of the column 

 is in ice water in some cases the animals do not ascend farther than 

 the level of the cold water on the outside of the glass. On the other 

 hand, some individuals, under similar conditions, will swim upward 

 through the remaining three-fifths of the column (although that part 

 is at room temperature) and will remain at the top for a short time. 

 But even when the entire container is immersed in ice water the 

 animals do not remain long at the upper levels, but gradually get 

 farther and farther away from the surface. A number of short ascents 

 may be made, but after each ascent the animal drops back a greater 

 distance than it swims upward, so that finally it reaches the bottom. 



It is evident, on the whole, that under the lighting conditions given 

 in table 8 there is a certain amount of reversal of geotropism from 

 positive to negative at the low temperatures. "When the water is cooled 

 and is also of high salinity (line 4), the behavior is substantially the 

 same as in cooled water of the usual degree of salinity (line 3). 



In vertical light from oelow (table 9). This experimental setting 

 does not apply to natural conditions but it is helpful for interpreting 

 behavior. In these tests the 15-watt lamp was used, and it was always 

 about fifteen centimeters from the center of the bulb to the bottom of 

 the aquarium. The containers were either museum cylinders, 35 by 6 

 centimeters, or tubes, 50 by 3 centimeters. 



As is shown in the first line of table 9 there is more movement 

 up than down at the usual temperatures and salinity. This is espe- 

 cially evident if line 1 is compared with the first lines of tables 6, 7 



