196 NATURAL HISTORY OF WASPS._ 
The regular arrangement of the upper part of the 
nest is much disturbed in the course of these events, 
and the top of one nest comes to look very like the 
top of another. But, at the bottom, at the growmg 
part of the nest, the different architectural instincts 
of the several species are displayed quite to the last. 
The number of layers of paper employed to form 
the nest-cover varies with the species, with the 
season, and with the circumstances under which the 
nest has been built. Sometimes the case is so thin 
that the comb shows an edge through the wall, 
while sometimes it is composed of as many as a 
dozen layers. But, however the thickness of the 
walls may vary, as a rule so invariable as to have 
been adopted as a means of classification, the combs 
of the nests of the Vespz have no connection with 
the outer case, except at the top of the nest. The 
comb and the case are mutually independent and 
separate from each other. 
The combs, unlike those of the honey-bee, are laid 
horizontally, stage below stage, each hanging from 
the one immediately above it, without any reference 
to the rest of the series. The two or three upper- 
most stages of comb, into which the first rudimen- 
tary cells have been expanded, are, in course of time, 
worked into the case of the nest at their edges. 
And the cells are cut down to allow room for the 
wasps to camp on the upper surface of the comb 
beneath. Wasps do not stand cold and wet, so a 
shelter is here provided for them, where they may 
be kept dry and warm, without interfering with the 
comfort and safety of the larve in the lower stages. 
Incidentally another advantage is gained by this 
