396 Universitii of California Puhlications in Zoology [Vol. 16 



the percentage distribution, by the number of times an excess of ani- 

 mals was observed in the upper or lower portions of the tubes, and bj- 

 the location of the center of distribution. Every experiment was con- 

 tinued as long as enough animals were alive to make it worth while — 

 in some cases to the next or even to the second day. So few observa- 

 tions were made after 8 p.m. that nothing need be said about them 

 except that they indicate that the descent begins before 9 p.m. 



At the lower temperatures, on the other hand, the ascent is much 

 less marked, although it can be said to occur. It is probably sig- 

 nificant that, in the lower half of the table, there is a gradual increase 

 in the percentages in the upper fifth of the tube accompanied by cor- 

 responding decreases in the lower fifth, from 8 a.m. to 6 p.m. Fur- 

 thermore, the pi-oportion of observations showing the excess in the 

 upper two-fifths increases during the time that the proportion in the 

 lower two-fifths steadily decreases. During these hours, also, the 

 center of distribution is gradually rising. All of these indications, 

 taken together, lead one to conclude that there is a certain amount 

 of upward movement. This conclusion is strengthened when it is 

 noted that from 6 to S p.m. the percentage distribution in section V 

 decreases, while that in sections IV, III, and I increases; that the 

 proportion of observations showing an excess of animals in the upper 

 two-fifths has decreased as compared with the preceding period, while 

 the proportion in the lower two-fifths has increased; and that the 

 center of distribution has been shifted to a lower level. Nevertheless, 

 the effect of lower temperatures is striking, on the whole. 



The upward movement in the dark is shown even more clearly 

 when the animals have been obtained from ten or twenty fathoms. 

 Temperature does not seem to affect such animals, but I have used 

 them only once when the temperature was 16° C or over. All records, 

 therefore, of the distribution of deep-water animals in the dark are 



TABLE 3 



ACAKTIA TONSA, ADULTS OF BOTH SexES, FROM 10-20 FATHOMS: SUMMARY OF 



Records of Dlstribution in a Column of Water in Darkness, 

 TO Show Effect of Time of Day 



