366 
STRANGE DWELLINGS . 
Now, if the real cause of the hexagonal form were to be found 
in the equal pressure of surrounding cells, the central cells 
of this group ought to be hexagons, for they are soft, pliable, 
and their conical form renders them peculiarly liable to be 
squeezed out of shape. Yet, on examining the nest, we find 
that all the cells retain their conical form, the central cells being 
as rounded as those on the exterior, and their mouths being as 
circular. 
These examples entirely destroy both theories. 
In the first instance we have nests of which the cells are per- 
fectly hexagonal throughout, although some of them are only 
attached by one side, and are not pressed upon at either of the 
five remaining sides. We find that the external angles are as 
sharp, and their internal measurement as true, as those which 
occupy the very centre of the bee-comb ; so that pressure is 
clearly not the cause of the hexagon. That excavation is not 
the cause is also evident, from the fact that the external cells 
cannot have been excavated, and yet are hexagonal. 
These examples, therefore, show that the hexagonal form can 
exist without pressure. But, as if to show that pressure can 
exist without producing the hexagonal form, we have the nest of 
the Mischocyttarus, whose long, delicate, soft-walled cells are 
grouped round each other, and yet retain their conical form, 
so that at any part of them a transverse section would show a 
circular edge. 
The insect which makes this nest is rather long, measuring 
perhaps an inch in length. The colour is pale yellow, and the 
abdomen is much elongated, and attached to a slender footstalk 
or peduncle nearly as long as itself. Several of the cells have 
been occupied by larvae which have begun to assume the pupal 
condition, as is shown by the white covers over their mouths. 
One of the most remarkable of these branch-building insects is 
that which has been appropriately named the Processionary 
Moth ( Cnethocampa processioned). This curious moth lays a 
number of eggs, mostly upon the oak, and as soon as they are 
hatched the little creatures begin to form their home. 
