136 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



ce./m. 3 at the Equator to 0.0150 cc./m. 3 at 12° N. 

 latitude). 



In this analysis no attempt has been made to 

 isolate the component of variance resulting from 

 time of day at which the hauls were made, and the 

 data are insufficient for a 4-way analysis. In table 

 14, however, the night samples are rather evenly 

 distributed throughout; e. g., the column for 

 series A, cruise 5, contains 8 night hauls and 1 

 twilight haul ; series A, cruise 8, contains 7 night 

 hauls and 4 twilight hauls ; series B, cruise 5, con- 

 tains 8 night hauls and 2 twilight hauls; and 

 series B, cruise 8, contains 9 night hauls and no 

 twilight hauls. As a consequence we might as- 

 sume that the day-night variation would tend to 

 cancel out. 



To test this assumption we have utilized the 

 values given in table 14, and at the expense of 

 considerable loss of data, we have constructed two 

 3-way tables, one including only day samples (ta- 

 ble 15) and the other only night samples (table 

 16) . An analysis of the day samples reveals quite 

 different results than does an analysis of the night 

 samples or of the combined day and night samples. 

 For the day samples we find no significant dif- 

 ferences (7 > >0.05) between series (longitudes), 

 between cruises, or among latitudes. An analysis 

 of the night samples provides the same conclu- 

 sions as were derived from the combined day and 

 night samples, there being no significant dif- 

 ferences (P>0.05) between series (longitudes) 

 but highly significant differences (P<0.01) be- 

 tween cruises and among latitudes. 



Table 15. — Analysis of variance of volumes (cc./m.') of 

 zooplankton samples taken in day hauls, cruises 5 

 and 8 



(Latitudes grouped to provide a value for each column; three criteria of 

 classification] 



Table 15. — Analysis of variance of volumes {cc./m. 2 ) of 

 zooplankton samples taken in day hauls, cruises 5 

 and S — Continued 



Table 16. — Analysis of variance of volumes (cc./m.') of 

 zooplankton samples taken in night hauls, cruises 5 

 arid 8 



[Latitudes grouped to provide a value for each column; three criteria of 

 classification] 



Least significant difference for latitudinal means = .0233 



"Indicates a highly significant (P<0.01) mean square value. 



Although it has been possible to utilize only a 

 portion of the data, the differences between cruises 

 and among latitudes may be regarded as real, for 

 they have been demonstrated not only in table 14 

 where the day-night component was present, but 

 also in the last analysis, table 16, where the day- 

 night component was removed. The evidence that 

 there is less latitudinal variation in the day 

 samples than in the night samples introduces 

 a new feature and reveals another possible source 

 of variation in the data. The cause, or causes, of 

 this phenomenon, if real, are as yet obscure to 

 the authors, but may be related to differences in 



