Avoiding here all repetition or recapitulation of our former narrative,
suffice it now to mention two interesting recent additions to our
knowledge, for which we are indebted to Mr. Darwin. One is a research, the
other an inspiration. It is mainly his investigations which have shown that
the glairy liquid, which is poured upon and macerates the captured insect,
accomplishes a true digestion; that, like the gastric juice of animals, it
contains both a free acid and pepsin or its analogue, these two together
dissolving albumen, meat, and the like. The other point relates to the
significance of a peculiarity in the process of capture. When the trap
suddenly incloses an insect which has betrayed its presence by touching one
of the internal sensitive bristles, the closure is at first incomplete. For
the sides approach in an arching way, surrounding a considerable cavity,
and the marginal spine-like bristles merely intercross their tips, leaving
intervening spaces through which one may look into the cavity beneath. A
good idea may be had of it by bringing the two palms near together to
represent the sides of the trap, and loosely interlocking the fingers to
represent the marginal bristles or bars. After remaining some time in this
position the closure is made complete by the margins coming into full
contact, and the sides finally flattening down so as to press firmly upon
the insect within; the secretion excited by contact is now poured out, and
digestion begins. Why these two stages? Why should time be lost by this
preliminary and incomplete closing? The query probably was never distinctly
raised before, no one noticing anything here that needed explanation.
Darwinian teleology, however, raises questions like this, and Mr. Darwin
not only propounded the riddle but solved it. The object of the partial
closing is to permit small insects to escape through the meshes, detaining
only those plump enough to be worth the trouble of digesting. For naturally
only one insect is caught at a time, and digestion is a slow business with
Dionaeas, as with anacondas, requiring ordinarily a fortnight. It is not
worth while to undertake it with a gnat when larger game may be had. To
test this happy conjecture, Mr. Canby was asked, on visiting the Dionaeas
in their native habitat, to collect early in the season a good series of
leaves in the act of digesting naturally-caught insects. Upon opening them
it was found that ten out of fourteen were engaged upon relatively large
prey, and of the remaining four three had insects as large as ants, and one
a rather small fly.
Public-domain text, read in full here on John Shaqi.
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