28 University of California Publications in Zoology [Vol.19 



from the pipes or from the ocean directly. It is possible to account 

 for some of the positive responses. When an animal is enclosed in 

 a tube that is horizontal with one end toward a light it may swim 

 • to the negative end and from there make short dashes toward the light 

 and back again to the end. The method of recording that I used makes 

 it possible to take note of such positive movements. I do not believe 

 that such behavior is due to positive phototropism. It is rather due 

 to the incessant activity, and after an animal has reached the end 

 of a tube it can only swim toward the light. Some cases, however, 

 are due to what seems to be a positive response, as such. If the animals 

 are tested soon enough after they come into the laboratory they are, 

 as already stated, usually positive, and some records of such animals 

 enter into the table. It has occasionally happened that an animal after 

 having gone from the light several times suddenly reversed and 

 traveled toward the light a few times and then returned to the former 

 kind of response. These records also are part of the first line in 

 table 4. But in general laboratory animals are strongly negative to 

 all intensities at ordinary temperatures and concentrations of the 

 water. 



If the results in the third line are compared with those appearing 

 in the first it will be seen that the differences in the percentages are 

 in favor of the positive instead of the negative side. That is, the 

 animals become positively phototropic in water of low temperature. 

 It was outside my purpose to try to ascertain the point at which there 

 appears a well defined positive reaction when the temperature is grad- 

 ually decreasing, or a negative reaction when the temperature increases 

 slowly. But table 5 (p. 30) will give the results of observing the 

 behavior of six animals in a dish while the temperature fell grad- 

 ually and then slowly rose. As usual, the dish was divided into five 

 sections, section I next to the light and section V opposite. In water 

 as cold as 6° C the animals swim around as freely and actively as 

 at 15° C. 



The table does not need further explanation. It shows the gradual 

 change from negative to positive as the temperature slowly decreases 

 and the reverse when it increases from the low points. Individuals 

 are continually swimming back and forth, and this accounts for most 

 of the animals noted in sections other than the one next the light, or 

 it is turned through 180° while the position of the light is not changed. 

 Or they will swim back and forth across the vessel when a 15-watt 

 lamp on one side is alternated with a 100-watt on the other, the move- 

 ment being toward the illuminated side of the aquarium. 



