345 



or.SlCIiVATIOXS ox THH FOOD OK ('I,A1 XICKKA. 



IIOMKK (;. FiSIlKK. 



During tlie \viii(cr <if li)i;Mi)14 I becaiue intoreslcd in llic fccdiiiji of two 

 six'cii's of {•ladocora (Dapliuia pulex and Siniocopliahis vctnlns) wiiidi were 

 licin- reared in the lalxirafory of Dr. A. M. Manta at the Station foi- 

 lOxi-eriniental Kvolutioii of the Carnegie Institution of Wasliington. It was 

 a part of my duty to conect food for tlieni and lienee the food was often 

 t>\a mined mieroseopieally, but by this nietliod I was unable to determine just 

 what elements of the mixture were beinj? used as food by the daphnids. 



At the sugsestion of Dr. Banta, I then tried to examine th(> contiMits of 

 tlie alimentary tracts of some of the daphnids, Init I was still unable at 

 tJiat 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 liaboratory of 

 Indiana University and during the following summer at the Indiana T'ni- 

 vcrsity Biological Station. At the Biological Station a third form. Dapluiia 

 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 wore 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 IS Daphnia pulex and 14 Simocephalus vetulus. 

 and at the Biological Staticn G4 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 w^ere collected from Eagle 

 (Winona) lake and from Cherry creek near its mouth. At the lake all of 

 the Daiihnia were obtained with a plankton pump from near the center of 

 tlie lake at a depth of 4-8 meters. The Simocephalus were collected with 

 a silk sampling net from the creek and from the edge of the lake among 

 the a<iuatic 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 shai)ed 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 



