INFLUENCE OF FOOD IN CONTROLLING SEX 547 



About five years ago the author had a general culture of 

 rotifers in a jar which was placed in a south window in the labora- 

 tory and rern.ained there during the spring months. Some time 

 in May during a period of a few days the jar was swarming with 

 countless numbers of the green flagellate, Dunaliella, Teodor 

 (Chlamydomonas, Cohn), On one day thirty-two female eggs 

 of the rotifers were taken from the surface of the culture water 

 and placed in watch-glasses and allowed to hatch. Each young 

 female matured and thirty (93 + per cent) of these females pro- 

 duced male offspring. This Dunaliella culture soon disappeared 

 and no other good one ever appeared again. However, the author 

 saved a little of the culture and spent the entire summer in the 

 attempt to grow pure or even mixed cultures of it. No medium 

 was found in which it would grow. 



This year another attempt has been made to grow cultures of 

 Dunaliella and has been quite successful although the method is 

 not yet completely perfected. They were raised in countless 

 numbers in direct sunlight and a solution of bouillon. An 

 Armoi.u''s bouillon cube was dissolved and boiled in 400 cc. of 

 tap water and equal parts of this bouillon solution and of steri- 

 lized water were used for the culture medium. The medium 

 was inoculated with a few individuals of Dunaliella and the jar 

 placed in a south window. Within 7 to 14 days the surface 

 of the culture water was swarming with the active Dunaliella 

 during the sunny part of the day. Toward night the animals 

 became inactive and motionless, in which state they remained 

 until the following morning and then only became thoroughly 

 active again provided there was direct sunlight. After the 

 culture became 2 to 3 weeks of age the Dunaliella would 

 remain continually in the motionless state. At this time the 

 old culture water was siphoned off and some new culture medium 

 was added to the quiescent Dunaliella. Within 2 to 3 days, if 

 in sunlight, practically all the Dunaliella would be active. The 

 surface was removed with a pipette and placed in a test-tube 

 and by centrifuging, all the Dunaliella were collected at the bot- 

 tom of the test-tube. Then nearly all of the liquid in the test- 

 tube was poured off, thus leaving the Dunaliella in enormous 



