90 University of California Publications in Zoology [Vol.22 



Ploima 



Station, I Station II Station III Daily Hourly 



Number of forms recorded 47 34 33 27 29 



Individuals per cu. meter.. 4,491,499 799,224 1,215,618 5,322,812 5,439,813 



Ploima were invariably present at all stations throughout the 

 year. The averages given above include the eggs, of which there were 

 about 30 per cent at Station I and Station III and over 40 per cent 

 at Station II. While the numbers were always rather large they were 

 especially so in temperatures above 15° C, the maximum at Station 

 I occurring in June at a temperature of 22.5° C, in November at Sta- 

 tion II at 19.5° C, in November at Station III at 17° C. A marked 

 preference for sewage is proved by the exceedingly large numbers at 

 Station I, median numbers at Station III and smallest numbers at 

 Station II. The large numbers in late summer and throughout the 

 autumn at all stations also indicate a favorable effect of stagnation. 



The fact that all the Ploima show strikingly uniform character- 

 istics of seasonal distribution, noted by Kofoid (1908) in Illinois is 

 strongly in evidence here, especially amongst the forms occurring 

 throughout the year. Plates 3, 4 and 5 give a graphic representation 

 of the occurrence of the group as a whole (including eggs) accom- 

 panied by a similar graph for the chlorophyll bearers. This does not 

 indicate any prominent relationship of the two groups. The follow- 

 ing text table gives the more prominent pulses of Ploima at Station 

 I (exclusive of eggs). Omission or inclusion of eggs does not affect 

 the location of the pulses, hence eggs are not segregated from other 

 records in totals at Stations II and III. 



Date No. 



Jan. 15 258,268 



Feb. 23 2,692,848 



Apr. 19 6,526.912 



June 25 .... 13,717,568 



Aug. 20 .... 5,287,904 



Nov. 19 .... 802,848 



It may be seen that of the seventeen pulses noted in this table 

 eight preceded chlorophyll and algal pulses by from three to twelve 

 days, usually three or four days. Coincidence occurred twice, and 

 there were two cases in which ploiman pulses followed the others by a 

 few days. In the other five cases no definite relation appeared. It 

 therefore seems that there is no such clearness of relationship of 

 pulses of Ploima and of chlorophyll bearers as was noted in Illinois 



