362 
STRANGE DWELLINGS . 
about one- third in proportion to the actual object. Several of 
these singular nests are in the collection at the British Museum. 
Occupying the lower part of the illustration is seen a leaf 
upon which are piled a number of fragments of leaves, so as to 
form a rudely conical heap. This is also the work of a spider, 
and is made with even more ingenuity than the two preceding 
specimens. In the first instance, the spider has spun a hollow 
case of silk, similar in principle of construction, though not in 
form, to the spherical egg cases made by several British spiders. 
In the second instance, the creature has chosen a number of 
concave seed-pods, and, by adjusting their edges together and 
fastening them with silk, made a ' hollow nest, which only 
requires to be lined in order to make it a fit nursery for the 
young. But, in the present example, the work of nest-making 
has been much more elaborate, for the structure has been re- 
gularly built up of a great number of pieces, each being arranged 
methodically upon the other, very much as children in the 
streets build their oyster-shell grottoes. The labour must have 
been considerable, even if the spider had nothing to do but to 
arrange and fasten together pieces of leaves which had already 
been selected. 
In the accompanying illustration three most remarkable nests 
are given, all of them the work of hymen opterous insects, and 
all serving in some degree to illustrate the hexagonal system of 
cell-building, so common among the hymenoptera. 
Of these, perhaps, the central figure is the most interesting, 
because it entirely sets at rest a question which is periodically 
agitated. It is made by an insect belonging to the genus Icaria . 
Perhaps my readers may remember that on a former page 
the celebrated bee-cell problem is described, and that mention 
is made of the many theories which have been invented to 
solve the riddle. Among them the two most conspicuous are 
those which are known as the equal pressure theory and the 
excavation theory. Differing as they do in many respects — one 
attempting to prove that each cell is forced into the hexagonal 
shape by the pressure of six cells surrounding it, and the other 
