70 Unwersity of California Publications in Zoology [Vol.22 



warmer weather or else its enemies multiply faster under such con- 

 ditions and so keep it down. The substantial agreement of Stations 

 II and III upon such a point in opposition to Station I makes it al- 

 most certain that sewage or organic content is in some way a more 

 influential factor than temperature in the warmer season. There 

 are some indications of recurrent pulses at all stations but they cannot 

 be readily followed through the year. Parasitized colonies were fre- 

 quently found, especially through the warm season. Eudorina is evi- 

 dently a more important planktont here than in Illinois except at 

 Station I where it is about the same. 



One experience in collecting at Station I gives some interesting 

 evidence as to the occurrence of swarms. The regidar collection was 

 taken near shore from the boat landing, one morning about 8 o'clock. 

 On examination of the living material under the microscope after 

 reaching home it was found to contain unusual quantities of Eudorina. 

 It seemed a favorable time to make a special collection to send to 

 Professor Kofoid so another trip was made to the same spot and 

 hauls taken as nearly as possible in the same way as before. Although 

 there had been a time interval of less than two hours scarcely any 

 Eudorina could be found anywhere about. Weather conditions had 

 not changed and there had been no great disturbance of the water by 

 boats as it was on a Sunday morning when the traffic was light. 



Euglena descs Ehrbg. 



Identification satisfactory. Loss through net heavy. Kecorded at 

 Station I five times and once at Station II. 



Euglena virfflis Ehrbg. 



Station I Station II Station III Daily Hourly 



Average 51,693 11,782 13,592 306,464 28,975 



Identification satisfactory. Probably very small percentage re- 

 tained by net. Occurs mainly in summer and early fall at all sta- 

 tions. Maximum in July at Station I and III, June at Station II. 

 Apparently favored by sewage, quiet water and temperatures above 

 20° C. Information from silk net catches not reliable beyond this. 



Hemidinium nasutum St. 



Station I Station II Station III Daily Hourly 



Average 535,079 28,482 26,967 228,971 293,432 



Identification doubtful. Very small percentage retained by net. 



Kecorded only in last half of year at all stations, possibly because not 



