288 THE EFFECT OF FOOD 



born obtain more nourishment, and develop into larger 

 females, which are capable of occasionally producing 

 females, as well as drones. Finally the future queens, 

 which obtain a still richer diet, are born. The deter- 

 mination of sex seems to be dependent on nutrition also 

 in aphides or plant-lice. Thus " during the summer 

 months, with favourable temperature and abundant 

 food, the aphides produce parthenogenetically genera- 

 tion after generation of females. The advent of au- 

 tumn, however, with its attendant cold and scarcity of 

 food, brings about the birth of males, and the conse- 

 quent recurrence of strictly sexual reproduction." * 

 In this instance, therefore, the effect of nutrition is 

 bound up with that of temperature, and there are no 

 data to show whether either of these conditions could 

 produce the effect if acting alone. 



Upon the Lepidoptera the effects of various foods 

 have been tested in a considerable number of instances. 

 Observations were made by G. Kochf in Germany as 

 long ago as 1832. By feeding the caterpillars of Che- 

 Ionia Jiebe with different plants, he obtained specimens 

 which were either fiery or dull red on the under wings, 

 and which varied in the extent of black marking and 

 white ground. In the case of Euprepia caja (Common 

 tiger moth) it is known, Koch says, " that when the 

 caterpillars are fed from their hatching to their meta- 

 morphosis with leaves of lettuce or deadly nightshade, 

 not one of the imagines produced resembles the origi- 

 nal form; when the insects have been fed on lettuce, 

 the white ground-colour of the wings predominates; 



*Ibid., p. 46. 



fEimer, " Organic Evolution," p. 149. 



