THE DETERMINATION OE SEX. 



39 



Von Siebold estimated the percentages of males and females in broods 

 of larvae reared from fertilized ova. The results of a series of obser- 

 vations may be condensed in a table : — 



As Rolph remarks, the results are not altogether satisfactory foi 

 the present purpose, ' ' but this much is clear, that the percentagt 

 of females increases from spring to August, and then diminishes. We 

 may conclude, without scruple, that the production of females from 

 fertilized ova increases with the temperature and with the food-supply 

 {Assimilations leisiung), and decreases as these diminish." 



From the work of Rolph, which is full ot suggestiveness which 

 the author unfortunately did not live to elaborate, we shall quote 

 another paragraph summing up further experiments of Von 

 Siebold: — 



"Not less instructive," he says, "are the experiments with 

 unfertilized ova (see Table). 



' ' This table shows the same general result as before. The more 

 abundant the metabolism (Stqffwcchsel~) and the nutrition, the greater 

 tendency to the production of females, which at the beginning and 

 at the end are wholly absent. In the above series of experiments, 

 they only appear when the metabolism and the nutrition were so 

 abundant that the entire development of the young wasps only 

 occupied eighteen or fewer days up to the period of pupation." 

 The peculiarity in this last case, if the experiments were correct, is 



