In November there is a great change and the rather meager 

 crustacean fauna contains only Epischura lacustris, Diaptomus 

 oregonensis , Cyclops bicuspidatus , Daphnia" (retrocurva ), and Bosmina 

 longirostris . Of these the only one present in any considerable 

 numbers is Diaptomus oregonensis . 



In December the Cladocera have entirely gone and the fauna 

 consists of Diaptomus oregonensis , D. mi nut us , Limnocalanus macrurus, 

 and a few immature Cyclops bicuspidatus. 



In this series of seasonal changes, the transition from the 

 restricted fauna of the winter to the abundance of summer and from 

 summer conditions to winter again is quite sudden, and we can almost 

 think of the fauna as having two seasons with the transitional months 

 of April and November, 



Quantitative Data 

 Island Section 



Horizontal Distribution 



Since plankton was first studied the question of the hori- 

 zontal distribution of plankton organisms has been a controversial one. 

 Prior to I892, according to Apstein (I896, p. $1), it was generally 

 held that the plankton of fresh water was not uniformly distributed 

 over wide expanses, but occurred in swarms in some parts of a lake and 

 only sparingly in others. Apstein believed that this conception arose 

 from the use of nets which were hauled horizontally. By the use of 

 vertical nets of the Hensen type, he was able to show that the plankton 

 of the Holstein lakes was distributed with a high degree of uniformity. 

 Since that time many students of the plankton have attacked the problem. 

 Some of those who have discussed it at length are Reighard (l89l0> 

 Ward (1896), Birge (I898), Marsh (1903), Moberg (I918), Bayersdoerfer 

 (I92U), Southern and Gardiner (1926), and Wilson (1929). 



Without discussing the findings of each writer, it may be 

 said that those who studied the volume of the total plankton 

 (plants and animals) were impressed by the essential uniformity of 

 distribution. There has been less agreement among -the students of the 

 zooplankton, and the last four papers cited emphasized the great 

 inequality of distribution of the Crustacea. It should be noted, however, 

 that Moberg, and Wilson, employed methods which must be regarded as in- 

 adequate for the problem in hand. Most of Moberg 's data were based on 



210 



