128 SOCIAL HABITATIONS. 
tract, and in a minute or two shrivels up into a flat 
membraneous mass, that looks like the web of the house- 
spider. M. Bosc was unable to rear any of the inmates 
of these galls. 
The size of a gall is no criterion of the dimensions or 
numbers of the insect which made it. Even in the galls 
which infest the oak, the smallest galls often furnish the 
largest insects, and in some specimens brought from 
Greece, the gall is as large as an ordinary black-currant, 
while the cell would contain a red-currant, showing 
that the inhabitant of the cell must be a large one in 
order to fill it. Again, although the oak-apple and 
rose-bedeguar do contain a great number of insects, there 
are many examples where galls scarcely so large as a pea 
contain from ten to fifteen insects, while the ink-gall 
and the large Hungarian gall are inhabited by a single 
insect. 
One of the most curious problems is, to my mind, that 
of the brilliant colours with which many of these galls 
are decorated. That the rose-bedeguar should be so 
beautifully adorned with scarlet and green is a fact 
which does not seem to excite any astonishment, inasmuch 
as it may be said that the colours which ought to have 
been developed in the petals and the leaves have been 
diverted from their proper course, and forced to exhibit 
themselves in the gall. 
Botanists and physiologists will see that this idea is 
quite groundless, but to the uninstructed and popular 
mind it has a sort of plausibility that often commands 
assent. But when we come to the oak-tree the case is 
at once altered, and some other cause must be found for 
the lovely colours of its galls. The cherry-galls are as 
brightly coloured as any apple, and the soft hues of the 
