bout the walls of its prison, which were quite hard and
smooth on the inside, probably owing to the movements of the larva, and
the consequent pressing of the sticky particles to the walls. In a short
time the opening made was closed over by a very thin silken web. The
cells, measured on the inside of the hard walls, were .35 of an inch in
length, and .15 in diameter. The natural attitude of the larva is
somewhat curved in its cell, but if straightened, it just equals the
inside length of the cell. On the 31st of July, two female bees came
out, having cut their way through the sides of their cells." In three
other cells "several hundred minute Ichneumons (Anthophorabia
megachilis) were seen, which came forth as soon as the cells were
opened."

The habits of the little blue or green Mason bees (Osmia) are quite
varied. They construct their cells in the stems of plants, and in rotten
posts and trees, or, like Andrena, they burrow in sunny banks. A
European species selects snail shells for its nest, wherein it builds
its earthen cells, while other species nidificate under stones. Curtis
found two hundred and thirty cocoons of a British species (Osmia
paretina), placed on the under side of a flat stone, of which one-third
were empty. Of the remainder, the most appeared between March and June,
males appearing first; thirty-five more bees were developed the
following spring. Thus there were three successive broods, for three
succeeding years, so that these bees lived three years before arriving
at maturity. This may partly account for _insect years_, which are like
"apple years," seasons when bees and wasps, as well as other insects,
abound in unusual numbers.

[Illustration: 26. Nest of Osmia.]

Mr. G. R. Waterhouse, in the Transactions of the Entomological Society
of London, for 1864, states that the cells of Osmia leucomelana "are
formed of mud, and each cell is built separately. The female bee,
having deposited a small pellet of mud in a sheltered spot between some
tufts of grass, immediately begins to excavate a small cavity in its
upper surface, scraping the mud away from the centre towards the margin
by means of her jaws. A small, shallow mud-cup is thus produced. It is
rough and uneven on the outer surface, but beautifully smooth on the
inner. On witnessing thus much of the work performed, I was struck with
three points: first, the rapidity with which the insect worked;
secondly, the tenacity with which she kept he