248 



PROBLEMS OF FERTILIZATION 



the percentage of eggs developing to larvae may be 

 as high by heat parthenogenesis as by fertilization, for 



31° C. THREE EXPERIMENTS 



Duration 

 OF Expo- 

 • SURE IN 



Minutes 



1-2 

 2^ 



3h 



4- 



5- 

 6. 



8. 



10 



12 



14-15 

 17-18 

 20-21 

 25-30 



Percentages of Eggs Forming Fertilization-Membranes and Larvae 



Experiment 2 



Experiment 3 



Membranes 



Ca. 



Ca. 

 > 



> 



Ca. 



o 

 o 



10-15 

 30-40 



70-80 



90 

 90 



QO 



100 



Larvae I Membranes 



Ca. 



Ca. 



> 



Ca. 

 Ca. 1 1 Ca. 

 20-30! Ca. 



Ca. 



o 



5 



50 

 60-70 



95 

 100 



100 



100 



100 



Ca. 90 



Ca. 75-80 



40-50 



Ca. 20 



Larvae 



O 



o 

 o 

 o 

 o 

 o 

 I 

 20 



60 



80-90 



50-60 



Ca. 10-15 

 o 



Ca. 

 Ca. 

 Ca. 



32° C. SIX EXPERIMENTS 



Dura- 

 tion of 



Expo- 

 sure in 

 Minutes 



1-3 

 4- ■ 



S-- 

 6.. 



7-. 

 8.. 

 10. 

 12. 



IS- 



Percentages of Eggs Forming Free-Swimming Larvae 



Exp. I 



o 

 Ca. I 

 Ca. 3-4 

 Ca. 35-40 



> 90 



85-90 



Exp. 2 



Exp. 3 



< I 



2- 3 



20-30 



70-80 



Ca. 95 



50-55 

 15-20 



o 



o 

 Ca. 4-5 

 15-20 

 55-60 

 95 

 75-85 

 25-35 

 <i 



Ca. 



Exp. 6 



O 



o 



10-15 



25-35 

 50-60 



80-90 



80-90 



Ca. 20 



it is rare to secure 80-90 per cent developing larvae 

 by fertilization with this material. (2) A short expo- 

 sure may cause membrane formation with no subse- 



