Diaptomus Pseudosanguineus Sp. Nov. 13 



Cyclops not active sexually; of the countless millions of females 

 practically none bearing eggs. "When one remembers how prolific these 

 creatures usually are this pronounced sexual impotence furnishes food 

 for thought. 



August 12. Pond almost dry, communicating with the permanent 

 pond by a very shallow neck of water; the hydrogen ion content PH 

 8.0; water almost void of cladoceran and copepodan life; repeated 

 hauls of the dredge discover a few specimens of each of Cyclopa ser. 

 Tulatus Fischer, Cyclops viridis (Jurine) var. insectus Forbes, Moina 

 brachiata (Jurine), all bearing eggs or young. 



Two weeks ago this pond was literally teeming with 

 life, today it is almost void of life. The explanation is as 

 f ollow^s : A succession of life appears in the pond. Cy- 

 clops viridis (Jurine) var. insectus Forbes gradually be- 

 comes the dominant form. One by one the species asso- 

 ciated with it die out until only Moina brachiata (Jurine) 

 survives. Cyclops viridus (Jurine) continues to multiply 

 until it is present in numbers unbelievably large, but 

 they are sexually impotent. In a few more days that 

 immense population disappears almost entirely. What 

 is the cause? The deaths during the early and inter- 

 mediate stages of the season may have been due to the 

 elimination of the vegetation, or to the rise in tempera- 

 ture, or to the fluctuations in the hydrogen ion content 

 of the water, but none of these factors accounts for the 

 catastrophic destruction of this Cyclops in the early part 

 of August. True the pond contained living grass at the 

 beginning of the history and no vegetation at the close, 

 tut Cyclops viridis (Jurine) is as much at home in water 

 free from vegetation as it is in the midst of water plants. 

 The pond was quite shallow at the time of the climax but 

 this copepod flourishes in the shallowest ponds as well 

 as in the deeper lakes. The temperature of the water 

 varied from 19°C to 17° and up to 35° but this species 

 of Cyclops thrives throughout that entire range. The 

 hydrogen ion content of the water descends from PH 

 7.9 to PH 7.0 and then ascends to PH 8.2 but this ento- 

 mostracan has been found breeding throughout tliat 

 entire range. When the pond contained multitudes of 



