411 



tity of water dipped from any part of the pond during this period always 

 contained them. They could be seen feeding at any time on vegetable 

 debris, Typha stems and algfe. 



During the spring of 1909 the number began to decrease, and in the 

 autumn they disappeared. They were never observed in 1910, although 

 the pond was examined for them many times. This fact has an important 

 bearing upon the general problem of distribution, as will be pointed out 

 later. 

 Cypris virens Jurine. 



This form has been present at all times but never developed in great 

 quantity. Its greenish color and the fact that it is more closely confined 

 to the substratum than Cypridopsis vidua, render it less conspicuous. 

 Cyclops serrulatus Fischer. 



Taken March 17, 1910, with eggs. Numerous in the shallower parts 

 of the pond during the latter part of the month. 

 Cyclops bicuspidatus Claus. 



The typical form "was present during the spring of 1910 but did not 

 occur in great numbers. 



Most females taken were carrying egg sacks. During July and August 

 as noted in the discussion of the plankton, this species occurred in great 

 numbers, the maximum being on August 12, when 704,600 per 100 liters 

 were present. However, the individuals were smaller and the stylets 

 shorter and relatively thicker than in the spring forms. 



Pearse ('05) reports this species as occurring in the spring in Ne- 

 braska. In the Illinois River, it is reported as a winter form, Kofoid ('03). 

 In Lake Michigan it is a summer form, Forbes ('82). In Wisconsin lakes 

 it is active in the cooler parts of the year and passes the summer in a 

 gelatinous cocoon. The seasonal distribution in different habitats of this 

 variable form offers an enticing problem. 

 Cyclops phaleratus Koch. 



Taken during March, 1910. Numerous April 15, 1911. Found among 

 Typha and near the edge of the pond. 



TARUIGRADA. 



Macrobiotus. 



A form which was referred to this genus was taken in the spring of 

 1910. They occurred in quantity on April 23, and for about one month 



