THE OSMIA. 245 
provisions, and closed perfectly, but yet the labour is not over, 
for the bee builds up a sort of roof or general covering to the 
whole, and uses larger sand grains than those which enter into 
the composition of the cells, and thus the external walls of the 
nests are found to have great thickness and wonderful hardness. 
The larve will have plenty to live upon, and certainly every care 
has been taken to place them out of danger. When they are full 
grown they add to their imprisonment by making a cocoon of a 
paper-like tissue, which looks as if it were varnished. Their 
metamorphosis is completed within, and the adult insects fly. 
But how do they manage to get out of their strong and prison- 
A NEST OF Chalicodoma muraria DETACHED AND SEEN FROM WITHIN. 
like home? Do they contrive to pierce the cement, which is as 
hard as stone, and which resists the blow of a hammer? Every 
care has been taken not to give too much trouble to the young 
bees in their first attempt at coming to the light. When the 
roof and general wall of the nest was constructed, a slit was 
left low down near each cell, and it forms a kind of door, hidden 
very carefully by rather soft sand or cement. 
It is very remarkable that this insect should not always build 
up its nest in the same manner, and that it should occasionally 
use the ruins of last year’s nests for the foundation and walls 
of the new. Old and more or less broken down nests, which 
contain vacant cells and the skins of the nymphs, frequently 
remain attached to walls, and the Chalicodoma, when exploring, 
