PROCESSIONAEY MOTH. 573 



base, and increases regularly towards the mouth, like a reversed 

 sugar-loaf. 



Now, if the real cause of the hexagonal form were to be found 

 in the equal pressure of sun'ounding ceUs, 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 

 circ\ilar. 



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 hexagoa 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. 



Oke of the most remarkable of these branch-building insecet is 

 that which has been appropriately named the Pkocessionary 

 Moth ( Cnethocampa processionea). 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. 



Externally it is not unlike that of the brown-tailed moth, but 



