which may be called the sublateral branch. There is also, on each side,
a main lateral branch or bundle, which bifurcates in the same manner as
the others. Bifurcation does not imply that any single vessel divides,
but that a bundle [page 248] divides into two. By looking to either
side of the leaf, it will be seen that a branch from the great central
bifurcation inosculates with a branch from the lateral bundle, and that
there is a smaller inosculation between the two chief branches of the
lateral bundle. The course of the vessels is very complex at the larger
inosculation; and here vessels, retaining the same diameter, are often
formed by the union of the bluntly pointed ends of two vessels, but
whether these points open into each other by their attached surfaces, I
do not know. By means of the two inosculations all the vessels on the
same side of the leaf are brought into some sort of connection. Near
the circumference of the larger leaves the bifurcating branches also
come into close union, and then separate again, forming a continuous
zigzag line of vessels round the whole circumference. But the union of
the vessels in this zigzag line seems to be much less intimate than at
the main inosculation. It should be added that the course of the
vessels differs somewhat in different leaves, and even on opposite
sides of the same leaf, but the main inosculation is always present.
Now in my first experiments with bits of meat placed on one side of the
disc, it so happened that not a single tentacle was inflected on the
opposite side; and when I saw that the vessels on the same side were
all connected together by the two inosculations, whilst not a vessel
passed over to the opposite side, it seemed probable that the motor
impulse was conducted exclusively along them.
In order to test this view, I divided transversely with the point of a
lancet the central trunks of four leaves, just beneath the main
bifurcation; and two days afterwards placed rather large bits of raw
meat [page 249] (a most powerful stimulant) near the centre of the disc
above the incision that is, a little towards the apex with the
following results:
[(1) This leaf proved rather torpid: after 4 hrs. 40 m. (in all cases
reckoning from the time when the meat was given) the tentacles at the
distal end were a little inflected, but nowhere else; they remained so
for three days, and re-expanded on the fourth day. The leaf was then
dissected, and the trunk, as well as the two sublateral branches, were
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