1914] Esterly: ScMzopoda of the San Diego Region 137 



meters as above 137 meters. The depth of the greater abundance for 

 daylight as shown in table 10 corresponds fairly well with that shown 

 in table 11, but it should be noted that the averages in line 6 of table 

 10 are per hour, while in line 4 of table 11 they are per meter. 



In section B of table 11, columns 1, 2, there is a large increase in 

 the number of animals taken, per meter of hauling, over the numbers 

 set down in the corresponding columns in section A. It is important 

 to note, furthermore, that the meter average in column 3 of section B 

 is but one-third as large as that in column 3 of section A. I believe 

 that this means that there is an actual decrease, after dusk, in the 

 number of animals below 275 meters, and that the increase indicated 

 in columns 1 and 2, section B, is due to migration of animals into 

 those levels from below. While there is some reason for saying that 

 animals tnight see the nets during the day at the surface, that will not 

 explain the decrease at night in deep water. If the organisms are 

 taken in larger numbers only when they cannot see the nets, there is no 

 reasonable explanation for the facts shown in sections A and B of the 

 preceding table. 



The records in section C of table 11 as compared with those in A 

 and B are indicative of the downivard movement that we should expect 

 if there is the upward movement at an earlier time. The meter 

 average in columns 1 and 2 of section C is considerably larger than 

 that in section A, but smaller than that in section B, and the same 

 relation holds between the frequencies. In column 3, however, the 

 average per meter is larger in section A than that in the others and 

 that in section B exceeds that in section C. I believe that these relative 

 figures mean that the movement toward deeper water begins before 

 2 a.m., and is not completed until after 6 a.m. 



A consideration of the occurrence of Nyctiphanes at the surface 

 must be confined to winter hauls, as is shown in table 4. The animals 

 were obtained only in November and December, but it seems fair to 

 consider all the winter months together. This is done in table 12. 



The table shows that Nyctiphanes is overwhelmingly more abund- 

 ant at the surface between 4 and 6 a.m. (line 12, colimins E and F). 

 We are not justified in assuming that that period really represents 

 the time of the surface plurimum, since it might occur during one of 

 the periods when no collecting was done. The table does not suggest, 

 in itself, that the organisms perform periodic vertical migrations, but 

 there is some evidence of this in the data concerning the hauls with 



