98 MALES AND FEMALES 



summer or autumn, and, unless one visits the 

 same spot again when both sexes are out, it is 

 impossible to associate males and females. I 

 have at the present moment in my collection 

 several males, which, being in doubt about 

 myself, I have communicated to continental 

 authorities, who have returned them to me as 

 possibly the male of so and so ! and we shall have 

 to remain in uncertainty about them till some one 

 happens to take both sexes together, when the 

 mystery will be solved. 



In time of appearance the males always pre- 

 cede the females in burrows, such as those of 

 the leaf -cutting bees, etc., it may seem puzzling 

 as to how this is arranged, as one cell is placed 

 over the other so that those lower down in the 

 tube cannot pass those higher up. This difficulty 

 is got over by the arrangement that the first 

 eggs laid by the mother bee are female and the 

 last male, so that those at the top belong to 

 this latter sex; these emerge as soon as the 

 warmth of the sun is great enough to energize 

 them sufficiently to break through their cell 

 covering, when they emerge and wait for the 

 appearance of their females. The males of 



