LIFE-HISTOEY OF EOTIFEE 237 



solution to 3, 4, 5 and 6 parts of spring water. Egg production 

 and the average length of life were both much reduced in this 

 medium and no change in the mature form or egg were pro- 

 duced. At various times throughout the experiment Proales 

 was cultivated in spring water in which various unicellular 

 green plants and animals were flourishing, but in all cases isolated 

 adults produced eggs of the usual thin-shelled form. In all 

 cases isolations were made for five successive generations, since 

 Shull ('12) has shown that the action of the environment is not 

 accompanied by a change in sex until grandchildren are produced. 

 .None of the changes in the nature or concentration of the food 

 were accompanied by the appearance of the male form in Proales. 



Cultures in re per cent malted milk, I per cent beef extract, and 

 in 1^ per cent pasteurized milk were subjected to a constant 

 temperature of ± 6°C., 17°C., 24°C., and to a fluctuating tem- 

 perature of 13° to 23°C. without producing any change in the 

 uniform female constitution of the population. 



In the summer of 1919, a number of mass cultures were estab- 

 Ushed in small watch-glasses; in each of these cultures there was 

 5 cc. of malted milk with sufficient of a t',j N solution of the 

 following chemicals to give the percentage (of Vo N) indicated. 



HCl, i, i i, 1, 2, 3 per cent KCl, i, i, f , 1 2, 3 per cent 



H2SO4, I, I, 1, 2, 3 per cent MgSO*, 2, 4, 6 per cent 



NaCl, 2, 4, 6 per cent K2HPO4, i f , 1, 2, 3 per cent 



C2H4OJ, i, i, f, 1, 2, 3 per cent NaNOs, 2, 4, 6 per cent 



At various times isolations were made from each culture; but 

 eggs were deposited by aU of the individuals and there was no 

 indication of the appearance of the male form. 



Thus, neither a change in the kind nor the concentration of the 

 culture medium, a constant or fluctuating change in the tempera- 

 ture, or a change in the chemical constitution of the medium, has 

 been accompanied by the appearance of the male in Proales 

 decipiens. 



In June, 1919, five 'wild' specimens of this species were found 

 in a culture jar filled recently with water from a small stream. 

 These organisms were transferred gradually to malted milk, and 



