HYMENOPTERA. 367 
of remark, that the head of the young is always turned down- 
wards, in such a way that it is by the bottom of its cell that it 
comes out. The bottom of the first is very near the surface of the 
wood, so that the insect it encloses has only a thin layer of wood 
to pierce through in order to set itself free. Each one of those 
which are born next has only to pierce the floor of its hiding- 
place to find the road before it free. The Xylocope pass the 











Fig. 340.—Mason Bee and Nest. 
winter in the pupa state, and the perfect insects, with wings of a 
beautiful metallic violet, appear in the spring, but are not found 
in this country. 
Other solitary bees have their hind legs unsuited for the gather- 
ing of pollen, but have the rings of the abdomen furnished with 
hairs for that purpose. Such are the Mason Bees of Réaumur, 
belonging to the genera Osmia and Chalicodoma,* which build their 
nests against walls with tempered earth, which become very hard. 
* At a meeting of the Entomological Society of London, Feb. 18th, 1867, Mr. 
Newman exhibited the lock of a door, one of several which, in 1866, were found at 
the Kent Waterworks, Deptford, to be completely filled and choked up with nests of 
