108 DAVID DAY WHITNEY 



EUCHLANIS DILATATA 



During the spring of 1916 Euchlanis dilatata appeared in sev- 

 eral of the battery jars of water that had been collected from 

 ponds in the vicinity of Middletown ; Connecticut. Small 

 amounts of fresh horse manure and small quantities of Chlamy- 

 domonas were occasionally added to these jars which were 

 allowed to stand in a large pan of running tap water in a south 

 window. After the jars had become more or less balanced and 

 contained several thousands of the rotifers which were almost 

 exclusively females greater quantities of Chlamydomonas were 

 added. Soon males began to appear and continued to increase 

 in numbers until in one experiment they composed 80 per cent 

 of the many thousands of individuals in the jar. When the 

 addition of Chlamydomonas was discontinued the males soon 

 disappeared and only females remained. The details of the ex- 

 periments are shown in table 3, a plotting of experiment 2 is 

 shown in diagram 3, and drawings of a female, male, and the 

 three kinds of eggs are shown in figure 3. 



BRACHIONUS MULLERI 



In September of 1916 water containing the marine rotifer, 

 Brachionus mulleri, was collected from a salt water lake near 

 Lincoln, Nebraska. Two to three liters of this water were put 

 into each of several battery jars and these were placed near a 

 west window but never received direct sunlight. Into some of 

 these jars a small amount of fresh horse manure was put and 

 into others small quantities of bouillon and stable tea. After 

 these jars had remained undisturbed for several days the rotifers 

 in them were examined and generally all or nearly all of them 

 were found to be carrying female eggs. Then during the fol- 

 lowing days bouillon or bouillon and stable tea together were 

 frequently added and soon the number of females carrying 

 female eggs began to decrease and females appeared carrying 

 male eggs. In some jars containing many thousands of females 

 the two kinds of females occurred in about equal numbers. In 

 one jar standing in sunlight and containing green microorgan- 



