MALE-PRODUCTION IN HYDATINA 151 



Why the 60 per cent oxygen in this experiment did - not in- 

 crease male-production, whereas the 40 per cent oxygen of the 

 preceding experiment did, is not known. Different concentra- 

 tions of the same agent may have different effects. Or oxygen 

 may increase male-production only when the other conditions 

 present are rather unfavorable to male-production. That the 

 other conditions were right for high male-production is shown 

 by the fact that the control line produced 26.8 per cent of male 

 producers, as against 7.4 per cent in Experiment 17. The stock 

 of rotifers used was, at the time of the experiment, in one of its 

 waves of high male-production. This may be the reason why 

 the oxygen could not still further increase the number of male- 

 producers. 



Experiment 19. Oxygen counteracting bouillon. This and the fol- 

 lowing three experiments were suggested by the possibility, mentioned 

 in the preceding paragraph, that oxygen could increase male-production 

 only when other conditions were rather unfavorable to male-production. 

 The several experiments immediately following show the influence of 

 oxygen in counteracting the effects of agents known to reduce the num- 

 ber of male-producers. 



In this experiment, a one-seventh per cent solution of Armour's beef 

 bouillon cubes was used. Only the parents were reared in the bouillon, 

 not the offspring (this being Whitney's method) . The parents were 

 put into bouillon for 10 to 14 hours, then transferred to a new dish of 

 bouillon. This transfer was made to insure that all the eggs laid in the 

 second dish went through their maturation stages in the bouillon. The 

 bouillon in the second dish was first saturated with an atmosphere con- 

 taining 40 per cent oxygen, and' the dish was then placed under a bell 

 jar, in a 40 per cent oxygen atmosphere. The parents remained in the 

 second dish for twenty-four hours, at the end of which time they were 

 removed. All the eggs laid in the second dish of bouillon were allowed 

 to hatch there, after which the young were transferred to spring water, 

 where they grew to maturity. 



The control parents were kept only in spring water which was kept 

 in ordinary air. Every time the parents in bouillon were transferred 

 to a new dish, the control parents were likewise transferred to fresh 

 spring water, to prevent the unequal accumulation of metabolic prod- 

 ucts in the two lines. 



Table 19 shows the results of the experiments. The oxygen 

 appears not only to have counteracted the effect of the bouil- 



