No. 403.] NOTES ON A SPECIES OF PELOMYXA. 
537 
going during August, there appeared in the early part of Sep- 
tember numbers of a large rhizopod belonging to Greef’s genus 
Pelomyxa. After discovering the presence of the form, I 
examined the tub systematically and found that the Pelomyxas 
were about evenly distributed over the wall, and in the stuff 
round the edge, but were not present over the bottom, where 
Tubifex had already made its appearance. They were abun- 
dant. On the average, each pipetteful of stuff (about 2 cc.) 
contained a specimen, which could be detected at once with the 
naked eye in a watch glass. In the same brown growth Szen- 
tor ceruleus was present in great numbers, and the Pelomyxas 
were feeding chiefly on these. In the Pelomyxas recognizable 
pieces of Stentor were commonly present, and sometimes a 
whole Stentor still rotating. Unlike the Pelomyxas previously 
described, this form contained no mud nor sand. 
The Pelomyxas continued to be abundant in the tub (preserv- 
ing the same distribution) for nearly two months. Towards 
the end of this time they began to disappear, the Stentors 
going first. With the gradual disappearance of these forms, 
Crustacea, particularly Cyclops, developed. The probable share 
that Cyclops had in the destruction of the Pelomyxas was indi- 
cated clearly in the following case. On September 8, ten 
Pelomyxas were transferred to a small glass aquarium jar, 
together with some of the brown “growth” and a little Spi- 
rogyra. They were supplied, during the first few days, three 
times with Stentors in considerable number. Within five days 
the Pelomyxas increased in number to fifty odd. After a week 
or two, Cyclops began to appear, and the Pelomyxas diminished 
in number and soon disappeared. I never actually saw Cyclops 
seize a Pelomyxa, but the former was constantly darting into, 
or “rooting” in, the stuff in which the rhizopods lay. And the 
only animals observed in the jar, besides Cyclops and Pelomyxa, 
were small Infusoria. 
In the following case the Pelomyxas obviously disappeared 
because of gradual starvation. In this case a number of the 
thizopods were transferred, in September, to glass preparation 
dishes, of a size (30 mm. X 70 mm. in diameter) that would per- 
mit examination under a low objective. Inthese dishes was kept 
