102 DAVID DAY WHITNEY 



There has also been carried on quite an extended series of 

 varied experiments with several species of rotifers to determine 

 the value of oxygen as a factor in causing male-producing females 

 to appear. The experiments with the four additional species of 

 rotifers concerning the production of male-producing females and 

 female-producing females by increasing or decreasing the food 

 supply will be presented first and following these there will be 

 presented the experiments with oxygen. The method of mak- 

 ing the stock bouillon, the stock stable tea, and of rearing pure 

 cultures of Chlamydomonas have already been previously de- 

 scribed in earlier papers. 



BRACHIONUS MILITARIS 



On January 7 of 1916 four liters of water and a small amount of 

 sediment were collected from a small pond near Middletown, 

 Connecticut. This collection was put into a battery jar which 

 was placed in a large pan of running tap water in a south win- 

 dow; thus allowing the jar to be in sunlight but at the same 

 time preventing any considerable rise in temperature by means 

 of the running water. A small amount of the stock stable tea 

 was added to the jar and then it was allowed to stand undis- 

 turbed during the remainder of January. During February 

 small quantities of Chlamydomonas were added to the jar and 

 on March 1 there were many thousands of females of Brachionus 

 militaris all of which were carrying female eggs. During the 

 following five days considerable quantities of the Chlamydomonas 

 were added daily to the jar and on March 6 about one-half of 

 the many thousands of females were carrying female eggs and 

 the other half were carrying male eggs. During the following five 

 days no Chlamydomonas was added and on March 11 about 90 

 per cent of the many thousands of females were carrying female 

 eggs and about 10 per cent were carrying male eggs. During 

 the following four days considerable quantities of the Chlamydo- 

 monas were again added and on March 15 about one-fourth of 

 the many thousands of females were carrying female eggs and 

 the other three-fourths were carrying male eggs. The complete 

 data of these experiments will be found in table 1, a plotting of 



