Quay, X. CONDUCTING TISSUES. 253 
cells are shown to be still more elongated; and these 
would form the most direct line of communication from 
the gland to the bending place of the tentacle. If the 
impulse travels down the exterior cells, it would have 
to cross from between twenty to thirty transverse par- 
titions; but rather fewer if down the inner parenchy- 
matous tissue. In either case it is remarkable that 
the impulse is able to pass through so many par- 
titions down nearly the whole length of the pedicel, 
and to act on the bending place, in ten seconds. Why 
the impulse, after having passed so quickly down one 
of the extreme marginal tentacles (about =; of an 
inch in length), should never, as far as I have seen, 
affect the adjoining tentacles, I do not understand. 
It may be in part accounted for by much energy 
being expended in the rapidity of the transmission. 
Most of the cells of the disc, both the superficial 
ones and the larger cells which form the five or six 
underlying layers, are about four times as long as 
broad. They are arranged almost longitudinally, 
radiating from the footstalk. The motor impulse, 
therefore, when transmitted across the disc, has to 
eross nearly four times as many cell-walls as when 
transmitted in, a longitudinal direction, and would 
consequently be much delayed in the former case. 
The cells of the disc converge towards the bases of 
the tentacles, and are thus fitted to convey the motor 
impulse to them from all sides. On the whole, the 
arrangement and shape of the cells, both those of the 
disc and tentacles, throw much light on the rate and 
manner of diffusion of the motor impulse. But why 
the impulse proceeding from the glands of the ex- 
terior rows of tentacles tends to travel laterally and 
towards the centre of the leaf, but not centrifugally, is 
by no means clear. 
