554 D. D. WHITNEY 



The author has several records of epidemics of males occurring 

 in his experiments during the last eight years at periods when 

 accidental rises of temperatures from 20+ to 26 or 27°C. took 

 place and while the food used was a mixed culture of green and 

 colorless Protozoa. These epidemics of males can be explained 

 in the same manner as the results of Maupas. At room tempera- 

 ture certain species of green Protoza were more or less quiescent 

 but when the temperature rose suddenly to 26+°C. all the 

 individuals of these somewhat quiescent green Protozoa became 

 very active and furnished a new diet for the rotifers. The 

 stimulation by this new diet caused the mothers to produce 

 male-producing daughters. After a few hours the temperature 

 sank back to the normal temperature of 20 + °C. and the remain- 

 ing green Protozoa again became quiescent and the rotifers were 

 forced to eat the other Protozoa that were normally active at 

 , this temperature and which was their regular diet. 



It has been previously observed that rotifers in a newly made 

 general culture of manure medium produce a much higher per- 

 centage of male individuals than rotifers in an old culture of 

 manure medium. It is generally known that in a newly made 

 hay infusion — and the same is true in a newly faade manure 

 infusion — the protozoan fauna fluctuates greatly. At first 

 individuals of certain species may be very abundant and later 

 individuals of other species became very numerous, while the 

 individuals of the earlier-appearing species in the culture become 

 relatively few. Thus there is a never-ending change in the 

 protozoan fauna in a new culture of water and manure. Certain 

 species flourish and are very abundant for a short period and 

 then they disappear and new forms replace them. When rotifers 

 are in such culture water with its varying protozoan fauna they 

 are, of course, subjected to many changes of diet. Some of these 

 changes of diet probably act as a stimulus upon the female roti- 

 fers so as to cause them to produce male-producing daughters 

 which produce males in the following generation. 



The sporadic production of males in the numerous experiments 

 of various workers who have used mixed protozoan cultures as 



