when first excited. Thus, when moderately large bits of meat were
placed on one side of the disc, and the discal and sub-marginal
tentacles on the opposite side became inflected, so that their glands
at last touched the meat and absorbed matter from it, they did not
transmit any motor influence to the exterior rows of tentacles on the
same side, for these never became inflected. If, however, meat had been
placed on the glands of these same tentacles before they had begun to
secrete copiously and to absorb, they undoubtedly would have affected
the exterior rows. Nevertheless, when I gave some phosphate of lime,
which is a most powerful stimulant, to several submarginal tentacles
already considerably inflected, but not yet in contact with some
phosphate previously placed on two glands in the centre of the disc,
the exterior tentacles on the same side were acted on.
When a gland is first excited, the motor impulse is discharged within a
few seconds, as we know from the [page 241] bending of the tentacle;
and it appears to be discharged at first with much greater force than
afterwards. Thus, in the case above given of a small fly naturally
caught by a few glands on one side of a leaf, an impulse was slowly
transmitted from them across the whole breadth of the leaf, causing the
opposite tentacles to be temporarily inflected, but the glands which
remained in contact with the insect, though they continued for several
days to send an impulse down their own pedicels to the bending place,
did not prevent the tentacles on the opposite side from quickly
re-expanding; so that the motor discharge must at first have been more
powerful than afterwards.
When an object of any kind is placed on the disc, and the surrounding
tentacles are inflected, their glands secrete more copiously and the
secretion becomes acid, so that some influence is sent to them from the
discal glands. This change in the nature and amount of the secretion
cannot depend on the bending of the tentacles, as the glands of the
short central tentacles secrete acid when an object is placed on them,
though they do not themselves bend. Therefore I inferred that the
glands of the disc sent some influence up the surrounding tentacles to
their glands, and that these reflected back a motor impulse to their
basal parts; but this view was soon proved erroneous. It was found by
many trials that tentacles with their glands closely cut off by sharp
scissors often become inflected and again re-expand, still appearing
healthy. One which was observed continued healthy for ten days after
219