If a vessel is placed under them in the evening,
it contains three or four pints of fluid in the morning. The natives
say that, if a drop falls into the eyes, it causes inflammation of these
organs. To the question whence is this fluid derived, the people reply
that the insects suck it out of the tree, and our own naturalists
give the same answer. I have never seen an orifice, and it is scarcely
possible that the tree can yield so much. A similar but much smaller
homopterous insect, of the family 'Cercopidae', is known in England as
the frog-hopper ('Aphrophora spumaria'), when full grown and
furnished with wings, but while still in the pupa state it is called
"Cuckoo-spit", from the mass of froth in which it envelops itself.
The circulation of sap in plants in our climate, especially of the
graminaceae, is not quick enough to yield much moisture. The African
species is five or six times the size of the English. In the case of
branches of the fig-tree, the point the insects congregate on is soon
marked by a number of incipient roots, such as are thrown out when a
cutting is inserted in the ground for the purpose of starting another
tree. I believe that both the English and African insects belong to the
same family, and differ only in size, and that the chief part of the
moisture is derived from the atmosphere. I leave it for naturalists to
explain how these little creatures distill both by night and day as
much water as they please, and are more independent than her majesty's
steam-ships, with their apparatus for condensing steam; for, without
coal, their abundant supplies of sea-water are of no avail. I tried
the following experiment: Finding a colony of these insects busily
distilling on a branch of the 'Ricinus communis', or castor-oil plant, I
denuded about 20 inches of the bark on the tree side of the insects, and
scraped away the inner bark, so as to destroy all the ascending vessels.
I also cut a hole in the side of the branch, reaching to the middle, and
then cut out the pith and internal vessels. The distillation was then
going on at the rate of one drop each 67 seconds, or about 2 ounces
5-1/2 drams in 24 hours. Next morning the distillation, so far from
being affected by the attempt to stop the supplies, supposing they had
come up through the branch from the tree, was increased to a drop every
5 seconds, or 12 drops per minute, making 1 pint (16 ounces) in every 24
hours. I then cut the branch so much that, du