It is interesting
to see two such widely different organs developed from a common origin; and
as the movable lip of the cell serves as a protection to the zooid, there
is no difficulty in believing that all the gradations, by which the lip
became converted first into the lower mandible of an avicularium, and then
into an elongated bristle, likewise served as a protection in different
ways and under different circumstances.
In the vegetable kingdom Mr. Mivart only alludes to two cases, namely the
structure of the flowers of orchids, and the movements of climbing plants.
With respect to the former, he says: "The explanation of their ORIGIN is
deemed thoroughly unsatisfactory--utterly insufficient to explain the
incipient, infinitesimal beginnings of structures which are of utility only
when they are considerably developed." As I have fully treated this
subject in another work, I will here give only a few details on one alone
of the most striking peculiarities of the flowers of orchids, namely, their
pollinia. A pollinium, when highly developed, consists of a mass of
pollen-grains, affixed to an elastic foot-stalk or caudicle, and this to a
little mass of extremely viscid matter. The pollinia are by this means
transported by insects from one flower to the stigma of another. In some
orchids there is no caudicle to the pollen-masses, and the grains are
merely tied together by fine threads; but as these are not confined to
orchids, they need not here be considered; yet I may mention that at the
base of the orchidaceous series, in Cypripedium, we can see how the threads
were probably first developed.
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