1914] Esterly : Schisopoda of the San Diego Region 141 



between 6 and 8 p.m. Nyctiphanes was found at the surface during 

 the winter, in larger numbers from 4-6 a.m., though a few animals 

 occurred as late as 10 a.m. (table 12). 



During the day in the winter months Euphausia appears to be 

 more abundant between 200 and 400 meters (table 10) and Nycti- 

 phanes between 101 and 200 meters (table 13), as shown by the collec- 

 tions with the Kofoid net. From 2-6 a.m. the average capture per 

 hour between 9 and 100 meters is very greatly increased over that 

 between 6 a.m. and 6 p.m. No hauls were made during the early 

 morning at depths below 100 meters, but what has been pointed out 

 is some indication that there is an upward movement of the animals 

 at night. 



The collections with the Nansen nets show that during the winter 

 and by day Euphausia is more abundant between 460 and 865 meters 

 (table 11, section A, column 4, line 4). From 6 to 10 p.m. the meter 

 average is higher, between 275 and 185 meters, and it is about six 

 times as great then as it is from 6 a.m. to 6 p.m. at that level, while 

 the evening meter average between 137 meters and the surface is twen- 

 ty-five times that during the day. At the same time (nightfall) that 

 the abundance increases above 275 meters, it decreases to a marked 

 degree as far down as 365 meters when compared with the day average. 

 This manner of occurence indicates that there is an upward movement 

 of the animals at dusk or soon after. The meter averages at depths 

 down to 365 meters are lower between 2 and 6 a.m., than at corres- 

 ponding levels from 6-10 p.m., but above 137 meters the average is 

 notably higher in the early morning than by day. This suggests that 

 the downward movement begins, roughly, between 10 p.m. and 2 a.m. 

 The small number of specimens of Nyctiphanes obtained with the 

 Nansen nets prevents an analysis of the occurrence of this form. 



The general indication for both Euphausia and Nyctiphanes is that 

 the animals do not remain during the night at the depths where they 

 are more abundant by day. This is in line with the suggested results 

 obtained by Holt and Tattersall (1905) and Fowler (1905). These 

 authors show, for several genera, that there is a rather strong prob- 

 ability that the animals move up at night and descend during the day ; 

 at the same time they are careful to recognise the possibility that the 

 failure to capture as many animals at or near the surface by day as by 

 night may be due to actual avoidance of the nets. The investigators 

 named do not admit, however, that their results can all be explained 

 on the ''avoidance" basis. 



