mere _lacunae_ traversing a rude tissue. Now countries in which
civilization is but commencing, display a like condition: there are no
roads properly so called; but the wilderness of vegetal life covering
the earth's surface is pierced by tracks, through which the distribution
of crude commodities takes place. And while, in both cases, the acts of
distribution occur only at long intervals (the currents, after a pause,
now setting towards a general centre and now away from it), the transfer
is in both cases slow and difficult. But among other accompaniments of
progress, common to animals and societies, comes the formation of more
definite and complete channels of communication. Blood-vessels acquire
distinct walls; roads are fenced and gravelled. This advance is first
seen in those roads or vessels that are nearest to the chief centres of
distribution; while the peripheral roads and peripheral vessels long
continue in their primitive states. At a yet later stage of development,
where comparative finish of structure is found throughout the system as
well as near the chief centres, there remains in both cases the
difference that the main channels are comparatively broad and straight,
while the subordinate ones are narrow and tortuous in proportion to
their remoteness. Lastly, it is to be remarked that there ultimately
arise in the higher social organisms, as in the higher individual
organisms, main channels of distribution still more distinguished by
their perfect structures, their comparative straightness, and the
absence of those small branches which the minor channels perpetually
give off. And in railways we also see, for the first time in the social
organism, a system of double channels conveying currents in opposite
directions, as do the arteries and veins of a well-developed animal.

These parallelisms in the evolutions and structures of the circulating
systems, introduce us to others in the kinds and rates of the movements
going on through them. Through the lowest societies, as through the
lowest creatures, the distribution of crude nutriment is by slow
gurgitations and regurgitations. In creatures that have rude vascular
systems, just as in societies that are beginning to have roads, there is
no regular circulation along definite courses; but, instead, periodical
changes of the currents--now towards this point and now towards that.
Through each part of an inferior mollusk's body, the blood flows for a
while in one d