410 



of these worms are always filled with decaying vegetable matter. They are 

 ravenously eaten by Amblystoma larvae, and Diemyctylus. These two facts 

 probably account for their occurrence in this limited habitat. 



CRUSTACEA. 



Arthropoda — 

 Daphnia pulex DeGeer. 



Occurred twice, in March and April, 1909, and in May, June and July, 

 1910. Its maximum occurrence was on June 15, 1910, when there were 80 

 per hundred liters of water. In towing collections, often but a single 

 specimen was taken. 

 Simocephalus vetellus Mueller. 



The most conspicuous crustacean of the pond. It is numerous at all 

 seasons among the plants and plant remains. It is rarely taken in the 

 open water of the central part of the pond. Adults were taken two days 

 after the rain which terminated the drouth in 1908. It was found that in 

 cultures it takes from 10 to 12 days for adults to develop. From these 

 facts, it appears that this crustacean was able to survive the drouth as an 

 adult. To do this, it must have worked its way down through the vege- 

 table debris to the water level. It is present at all periods of the year, 

 producing a maximum of 25 young in a brood. It makes a slight diurnal 

 vertical migration. This is difficult to demonstrate quantitatively because 

 of its habitat. If the surface of the water be "skimmed" with a fine 

 meshed net during the day, very few if any individuals are taken. How- 

 ever, many individuals are taken by this operation at any hour of the 

 night during the summer months. 



Alona quadrangularis Miiller. 



Appeared in March, 1910. Taken with young in brood chambers. 

 Never more than 120 per hundred liters until May 28, when 696 per hun- 

 dred were taken. It varied during June, July and August from 500 to 780 

 per hundred liters, the maximum occurring on Aug. 12. Eggs were present 

 in brood chambers in a large per cent, of them from April till August of 

 this year. i. 



Cypridopsis vidua Brady. 



Appeared as soon as the pond began to fill with water in Nov., 1908. 

 During the following winter and spring it was one of the most conspicuous 

 forms. No attempt was made to estimate its numbers, but a small quau- 



