Bramble-bees and Others 



that a second row of cells is placed above the 

 first row backing on to that plane; a third 

 row occurs less often. The nest is then one 

 of several storeys. The lower storeys, the 

 older, contain only females; the upper, the 

 more recent storey contains none but males. 

 It goes without saying that the surface layer, 

 even of the lower storeys, can contain males 

 without invalidating the rule, for this layer 

 may always be looked upon as the Chalico- 

 doma's last work. 



Everything therefore contributes to show 

 that, in the Mason-bee, the females take the 

 lead in the order of primogeniture. Theirs 

 is the central and best-protected part of the 

 clay fortress; the outer part, that most ex- 

 posed to the inclemencies of the weather and 

 to accidents, is for the males. 



The males' cells do not differ from the 

 females' only by being placed at the outside 

 of the cluster; they differ also in their capa- 

 city, which is much smaller. To estimate the 

 respective capacities of the two sorts of cells, 

 I go to work as follows : I fill the empty cell 

 with very fine sand and pour this sand back 

 into a glass tube measuring 5 millimetres^ in 



^.195 inch. — Translator's Note. 



116 



