626 THE PHYSIOLOGY OF REPRODUCTION 



improbable in the cases described that it could have been 

 reversed after having been difEerentiated. Furthermore, experi- 

 ments by Briggs ^ and other investigators have failed to support 

 the hypothesis that the proportion of the sexes can be altered by 

 modifying the diet, while KeUogg ^ has shown that in the case 

 of the silkworm moth, sex is definitely determined as early as 

 immediately after the first larval moulting, this conclusion being 

 based on an examination of the rudimentary reproductive glands. 



According to Cuenot ^ the essential organs of reproduction 

 in the maggots of flies are not difEerentiated into ovaries or 

 testicles until a late period of larval development. There was 

 a possibiUty, therefore, that in these animals the sex coxild be 

 modified by the conditions of nutriment or other external 

 factors. Cuenot found, however, that the proportion of the 

 sexes was not materially affected by the supply of nourishment, 

 although the maggots were fed upon different kinds of food, 

 some being given brain, suet, and a little meat, some a large 

 supply of putrefying flesh, while others were relatively starved. 



Among bees and other hymenopterous insects the nutriment 

 appears to be the main factor determining the difference be- 

 tween the two kinds of females (workers and queens). A 

 worker larva can be made to develop into a queen by supplying 

 " royal food," that is, food which is given to young queens. 

 In the worker the female generative organs never fully develop, 

 but royal diet stimulates these organs to grow so that the larvae 

 become queens. A partially developed worker may be made 

 partially fertile by supplying it with some of the jelly obtained 

 from a royal cell. The following table shows the relative com- 

 position of the sohd food given to workers and queens : * — 



This table shows that the quantity of fatty material suppHed 



1 Briggs, " Notes on the Influence of Food in Determining the Sexes of 

 Insects," Trans. Entom. Soc, London, vol. i., 1871. 



^ Kellogg, " Notes on Insect Bionomics,'' Jour. ofExper. Zoo}., vol. i., 1904. 

 ■> Cuenot, loc. cit. * Geddes and Thomson, loc. cit. 



