370 University of California Publications in Zoologn [Vol.22 



GENERAL DISCUSSION 



Through the first eight months of 1920 collections were taken at 

 intervals of twelve hours at the La Jolla pier. Since such a series 

 cannot properly be compared with one taken at different intervals, this 

 series may best be segregated and discussed first merely as a twelve- 

 hour series. The morning catches can then be properly included in 

 a separate discussion of the twenty-four-hour series taken at both 

 stations. 



The Twelve-Hour Series 



Attention will here be limited to features peculiar to the twelve- 

 hour series. These features are all connected with the question as to 

 whether larger numbers of diatoms and dinoflagellates were taken in 

 morning or in evening catches. This question has already received 

 some attention (Allen, 1922). 



Summaries now available for the twelve months from September 1, 

 1919, to September 1, 1920, show a rather marked difference in 

 diatoms and dinoflagellates, the former being taken in larger numbers 

 in morning catches, the latter in evening catches. This fact is b'est 

 shown by comparing single catches with the two nearest, i.e., twelve 

 hours earlier and twelve hours later. Thus, in the case of diatoms, 

 in the twelve months, 146 morning catches were larger than the two 

 nearest evening catches while only 62 evening catches were larger 

 than the two nearest morning catches. But, in the case of dino- 

 flagellates, only 86 morning catches were larger than the two evening 

 catches while 135 evening catches were in excess of the two morning 

 catches. 



Similar differences appear when comparing catches with the last 

 one preceding them. Thus, in the twelve months, each of 224 morn- 

 ing catches of diatoms exceeded that taken the evening before and 

 only 136 of the evening catches exceeded those taken respectively the 

 mornings before, while four were equal. But, in the case of dino- 

 flagellates, only 163 of the morning catches exceeded those respectively 

 of the preceding evenings, while 198 of the evening catches exceeded 

 those respectively of the preceding mornings, four being equal. 



