Bramble-bees and Others 



though the nests were removed from their 

 pebbles on the spot. 



From the enormous number of nests which 

 I have examined, I am able to state that, when 

 the cluster is regular, the female cells occupy 

 the centre and the male cells the edges. 

 Where the irregularity of the pebble has pre- 

 vented an even distribution around the initial 

 point, the same rule has been observed. A 

 male cell is never surrounded on every side 

 by female cells: either it occupies the edges 

 of the nest, or else it adjoins, at least on 

 some sides, other male cells, of which the last 

 form part of the exterior of the cluster. As 

 the surrounding cells are obviously of a later 

 date than the inner cells, it follows that the 

 Mason-bee acts like the Osmiae : she begins 

 her laying with females and ends it with 

 males, each of the sexes forming a series of 

 its own, independent of the other. 



Some further circumstances add their tes- 

 timony to that of the surrounded and sur- 

 rounding cells. When the pebble projects 

 sharply and forms a sort of dihedral angle, 

 one of whose faces is more or less vertical 

 and the other horizontal, this angle is a fa- 

 vourite site with the Mason, who thus finds 



114 



