OBSERVATIONS ON THE FOOD OF CLADOCERA. 
BY THE LATE 
_ Homer G. FISHER. 
During the winter of 1913-1914 I became interested in the feeding of two 
species of cladocera (Daphnia pulex and Simocephalus vetulus) which were 
being reared in the laboratory of Dr. A. M. Manta at the Station for 
Experimental Evolution of the Carnegie Institution of Washington. It was 
a part of my duty to collect food for them and hence the food was often 
examined microscopically, but by this method I was unable to determine just 
what elements of the mixture were being used as food by the daphnids. 
At the suggestion of Dr. Banta, I then tried to examine the contents of 
the alimentary tracts of some of the daphnids, but I was still unable at 
that time to arrive at any definite conclusion as to what constituted their 
food. The only organized material that I was able to make out was a very 
minute organism that I supposed to be a bacterium. These observations 
were extended during the following year at the Zoological Laboratory of 
Indiana University and during the following summer at the Indiana Uni- 
versity Biological Station. At the Biological Station a third form, Daphnia 
hyalina, was studied. 
The method has been to examine the alimentary tracts as soon after feed- 
ing as possible to determine what had been ingested. At the University 
Laboratory the daphnid was always rinsed in tap water, placed on a clean 
slide, and crushed with a clean cover slip. In this manner most of the 
material of the alimentary canal was expelled and made available for 
observation. At the Biological Station the same method was used except 
that the animal was allowed to swim in distilled water a few minutes before 
it was put on the slide. Additional studies were made by making smears 
of the alimentary tract and staining. The stain used was in every case 
Flemming’s triple stain. The following species and numbers were ex- 
amined; at the Station for Experimental Evolution about 15 individuals, at 
the University Laboratory 18 Daphnia pulex and 14 Simocephalus vetulus, 
and at the Biological Staticn 64 Daphnia pulex, 17 Simocephalus vetulus, 
and 3 Daphnia hyalina. They were all parthenogenetic females. ’ 
At the Station for Experimental Evolution the daphnids were all obtained 
from laboratory jars. At the University they were. obtained from Hill 
Pond, and at the Biological Station they were collected from Eagle 
(Winona) lake and from Cherry creek near its mouth. At the lake all of 
he Daphnia were cbtained with a plankton pump from near the center of 
the lake at a depth of 4-S meters. The Simocephalus were collected with 
a silk sampling net from the creek and from the edge of the lake among 
the aquatic plants. The material was examined as soon after collection 
as was practicable. 
The only organized material found in the intestine of any of the species 
was a minute pear shaped flagellate, the systematic position of which has 
not been determined. There may be two or more species of the flagellates 
but they are so minute that it is not possible at present for me to determine 
