THE FACTORS WHICH DETERMINE SEX 627 



to the developing queens is very nearly double that given to the 

 workers. 



There is no evidence that drone larvse can be converted into 

 females by a supply of royal or other food, so that the case of 

 bees can scarcely be regarded as affording a real instance of sex 

 being determined by conditions of nutrition, since workers are 

 true females whose reproductive organs and other sexual char- 

 acteristics have failed to develop owing to an insufficiency of 

 stimulating food. 



The case of white ants or termites is probably comparable, 

 though considerably more comphcated, since the different kinds 

 of sexual individuals are more nunierous. The young may 

 develop into workers, soldiers, or royal substitutes, and the 

 latter may be further transformed into fully fertile or " royal " 

 individuals, while both sexes (i.e. males and females) are 

 represented in each of these forms. Grassi's observations ^ point 

 strongly to the conclusion that these different kinds of indivi- 

 duals are developed from similar eggs under different condi- 

 tions of nutrition which is supphed to the young by the older 

 members of the community ; but here again there is no evidence 

 that males can be converted into females or fenjales into 

 males. 



Rolph 2 has described a series of observations on the pro- 

 duction of males and females in Nematus ventricosus, a species 

 of wasp. These observations show that the percentage of 

 females in broods of larvse reared from fertihsed ova steadily 

 increased from June to August and then proceeded to diminish. 

 " We may conclude without scruple, that the production of 

 females from fertihsed ova increases with the temperature 

 and Avith the food supply (Assimilationsleistung), and de- 

 creases as these diminish." ^ Certain further experiments with 

 unfertihsed ova of the same species seem to show that " the 

 more abundant the metabohsm (Stoffwechsel) and the nutrition, 

 the greater the tendency to the production of females." In the 

 normal condition males only were produced as a result of 



' Grassi and Sandias, " The Condition and Development of the Society of 

 Termites," Quar. Jour. Micr, Science, vols, xxxix. and xl., 1896-97. 

 ^ Eolph, Biologische Probleme, Leipzig, 1884. 

 ' Translated by Geddes and Thomson. 



