4 Vnivcrsiiy of California Puhlicaiions in Zoology. [^^♦^l. 8 



p.m. These surface hauls do not help us to understand why such 

 distribution should occur, but it may be said that light does not 

 appear to have any influence. 



It is worthy of remark that the surface haul that took the 

 largest number of Eucalanus also took more Calamis finmarchicus 

 than any other haul; there is thus an indication that the condi- 

 tions which are particularly favorable for surface aggregations 

 of one species are in some cases favorable for another species. 

 This is not always true, because two other very large surface 

 collections of Calanus did not contain any Eucalanus. I have 

 been unable to find a clue, thus far, as to the conditions that 

 favor accumulations of the latter species at the surface. When 

 we consider that Eucalanus was uniformly absent from collec- 

 tions with the closing net at levels down to ten fathoms (Table 2, 

 line 2), it seems strange that the species should have occurred at 

 all at the surface. This may be connected with the difference 

 between the areas of the two sorts of nets. 



The plurimum for Eucalanus during daylight is at about 200 

 fathoms. Though in the table (column A, line 7) it would seem 

 to be between 200 and 250 fathoms, five hauls at 200 fathoms took 

 3640 per hour during the day and one haul at 250 fathoms did 

 not take any; it seems fair, therefore, to conclude tliat the depth 

 at which the animals are most abundant during the day is 200 

 fathoms. 



It is plain from Table 2 that Eucalanus does not exhibit any 

 well-marked diurnal migration. There are no significant in- 

 creases in daily averages at any level after 6 p.m., and if vertical 

 migrations really occur we could reasonably expect that fact to 

 be indicated somewhere in the amount of data available. If a 

 change in the number of animals taken per hour may be regarded 

 as showing that there is a movement of the species, Table 2 shows 

 that fact most clearly, but the movement does not appear to be 

 away from the lower levels at twilight or later in the night. If 

 columns A and B of the table and lines 3 to 7 are compared, it 

 will be seen that in every ease the hourly averages are smaller in 

 the early portion of the night than during the day. There is 

 hardly any other conclusion to be drawn than that there is some 

 movement of the species as a whole which leads to a decrease in 



