44 



THE EVOLUTION OF SEX. 



brood. These are not too abundantly supplied Avith nourish- 

 ment, the queen having much upon her shoulders ; they develop 

 into small females, workers in a sense, but yet fertile, though 

 only to the extent of producing drones. By-and-by a second 

 brood of workers is born; these have the advantage of the 

 existence of elder sisters, are more abundantly nourished, and 

 develop into large females. Still, like the first brood, they pro- 

 duce drones, though occasionally females. Finally, with the 

 advantage of two previous broods of small and large females, 

 the future queens are bom. The above facts not only afford 

 an interesting corroboration of the influence of nutrition upon 

 sexuality, but are of importance as suggesting the origin of the 

 more highly specialised society of the hive bee. 



(<:) Von Siebold's Experiments. — With a somewhat different purpose 

 than that at present pursued,. Von Siebold made a series of careful observa- 

 tions on a species of wasp, Nematus ventricosiis. These afford, as Rolph 

 has noted, some valuable results in regard to the determination of sex. In 

 this wasp, the fertilised ova, unlike those of hive bees, develop into males 

 as well as females ; while the unfertilised, or parthenogenetic eggs, may pro- 

 duce females in small percentage. From spring onwards, as warmth and 

 food both increased, Von Siebold estimated the percentages of males and 

 females in broods of larv^ae reared from fertilised ova. The results of a 

 series of observations may be condensed in a table : — 



End of Larval period 



Percentage of 



Xo. of 



No. of 



(Pupation). 



Females. 



Females. 



Males. 



15th June 



14 



19 



136 



uly 



77 



66 



66 



.uly 



269 



579 



215 



August 



340 







End of August 



500 







September 



100 







As Rolph remarks, the results are not altogether satisfactory for the 

 present purpose, "but this much is clear, that the percentage of females in- 

 creases from spring to August, and then diminishes. We may conclude 

 without scruple, that the production of females from fertilised ova increases 

 with the temperature and with the food supply {Assi/nilationsleishing), 

 and decreases as these diminish." 



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

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

 paragraph summing up further experiments of Von Siebold : — 



"Xot less instructive," he says, "are the experiments with unfertilised 

 ova (see Table). 



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

 abundant the metabolism [Stoffwecksel) and the nutrition, the greater 



