433 
whether animal or vegetable, living within or upon another 
organism which serves as a host, at that host’s expense— appro- 
priating to its own uses the juices of the host, to the host’s 
detriment ; and giving back nothing in return towards the host’s 
support. Of this mode of life we have among both plants and 
animals many examples j notably, the Fluke in Sheep, which, 
favoured by the late wet seasons, has wrought so much mischief 
among our flocks. Among vegetables the Broomrapo {Orohanche), 
whose seed, incapable of its own support, germinates on the root of 
its host, then flourishes and flowers at its host’s expense. Again, 
we know what Commensals {Messmates) are, which, living together 
to their mutual advantage, draw their sustenance from a common 
source, probably always helping one another in some way. Of 
these, among animals, there are many examples ; — the Pea Crab 
for instance, which lives in tlio ^fussel’s shell ; the Mussel provides 
the house, and tho Crab helps in the housekeeping. Among 
vegetables Epipliytes seem to take tho place of Commensals. 
Orchids, for example, grow on tlie boughs and trunks of living 
trees, subsisting with them on tho atmospliore and moisture around, 
but drawing no sustenance from tho life of their apparent host, for 
they will grow equally well on a bit of dead wood. But in that 
form of Symbiosis which we are considering, tho plant lives within 
tho animal morphologically, apparently an entozoic parasite ; 
physiologically, an independent being both contributing to each 
other s support, yet either capable of independent life, but “ living 
in common ” to their great mutual advantage. 
During the past year two very remarkable sets of observations 
on this subject have been published one by Herr Brandt, in 
communications to the Physiological Society at Berlin, summarized 
in the ‘Transactions’ of the Royal Microscopical Society j tho other 
by Mr. Patrick Geddes, in communications to the Royal Society of 
Edinburgh, inserted in ‘Mature.’ It has long been known that 
many of tho lower animals contain granules of chlorophyll, and it 
has been found that this chlorophyll, tested by the spectroscope, 
is chemically identical with the true chlorophyll of green leaves, 
and seveml theories have been advanced to account for the presence 
