62 University of California Publications in Zoology [ VoL - 19 



ment through the cold water leading to the distribution recorded in 

 line 17 as compared with that in line 16. 



Line 18 is of interest as showing that Sagitta may remain nega- 

 tively geotropic in darkness for five hours ; at least it may reasonably 

 be assumed that there was no marked downward movement from 

 3 :25-8.20 p.m. 



Table 24 shows finally that specimens of this chaetognath may 

 exhibit the same kind of behavior late on the day after their removal 

 from the ocean that they did within the first hour. 



In giving the results of similar experiments on a second set of 

 twenty animals it is not necessary to go into so much detail as in 

 table 24. The observations are summarized in table 25 ; there were 

 alternating periods of diffuse light and darkness and all the records 

 obtained under each condition are put together in the several divisions 

 of the table. The experiments were carried on in a room with white 

 walls and lighted by four tall north windows. The container was a 

 cylinder 50 by 6 centimeters and the animals were put into it within 

 half an hour of the time they were taken. 



There is always more marked negative geotropism in darkness than 

 in the light, regardless of the temperature. This is shown by the 

 percentages and also by the centers of distribution. But it is evident 

 that most of the animals do not descend in the light into the colder 

 water. In sections b and c of the table most of the animals are shown 

 to be in that fifth of the cylinder which is immediately above the upper 

 limit of the cold water, during the time that the specimens were ex- 

 posed to the light. In the first line of b in the table a larger propor- 

 tion of animals is recorded in the middle section of the cylinder than in 

 all the others in c most of the animals were in the upper section dur- 

 ing the time they were in the light. "When the temperature of the 

 lower sections of the cylinder was higher more animals descended into 

 those levels in the light. 



SUMMAEY 



It has been shown by the experiments: (1) Sagitta is strongly 

 positive to light ranging from that of a 15-watt lamp at 50 centi- 

 meters to daylight about 3800 times as intense. No tests were made 

 with intensities beyond these limits. (2) The geotropism is predomi- 

 nantly negative in darkness and in light that is not too bright. In a 

 room with white walls and well lighted from without the geotropism 



