632 PRACTICAL PROBLEMS 



In plant lice. 1 In general it may be said that in summer, 

 when favorable conditions of life are at the maximum, these 

 creatures produce parthenogenetically generation after genera- 

 tion, and only females, but with the cool of autumn and its 

 lessened food supply, males appear, and sexual reproduction is 

 resumed ; indeed, to quote from Geddes and Thomson, 2 " in 

 the artificial environment of a greenhouse, equivalent to a per- 

 petual summer of warmth and abundant food, the partheno- 

 genetic succession of females has been experimentally observed 

 for four years. It seems in fact to continue until lowering of 

 the temperature and diminution of food reintroduce males and 

 sexual reproduction." Others have stated that males may be 

 produced at any time merely by letting the plants on which the 

 lice are feeding become somewhat "dried up." 



SECTION III INFLUENCE OF FERTILIZATION 



In bees. 3 As is now well known, bees are of three forms as 

 regards sex, drones (males), produced from unfertilized eggs ; 

 workers (females, generally but not always sterile), produced 

 from fertilized eggs ; and queens (fertile females), also pro- 

 duced from fertilized eggs but quartered in special cells and 

 given large amounts of special food. As remarked by Geddes 

 and Thomson, " royal diet and plenty of it develops the repro- 

 ductive organs of the future queens," and at any time " within 

 the first eight days of larval life the addition of a little food will 

 determine the striking structural and functional difference 

 between worker and queen." 4 This fact is often taken advan- 

 tage of by the nurse bees when disaster threatens through the 

 loss of the queen cells. Hastily extracting some worker larvae 

 from their ordinary cells, they deposit them in the queen cells, 

 giving them royal food, and speedily they acquire all the charac- 

 ters of any other fertile queen, a result plainly due either to 

 the character or to the quantity of the food, or to both. 



In the case of bees, therefore, fertilization seems to be the 

 deciding factor as to differences between male and female, and 



1 Geddes and Thomson, The Evolution of Sex, p. 49. 



2 Ibid. p. 50. 3 Ibid. pp. 46-48. * Ibid. p. 47. 



