be. Such moving
filaments, and such rings, are described by those, who have attended to
microscopic animalcula. This living ring may now embrace or absorb a
nutritive particle of the fluid, in which it swims; and by drawing it into
its pores, or joining it by compression to its extremities, may increase
its own length or crassitude; and by degrees the living ring may become a
living tube.

2. With this new organization, or accretion of parts, new kinds of
irritability may commence; for so long as there was but one living organ,
it could only be supposed to possess irritability; since sensibility may be
conceived to be an extension of the effect of irritability over the rest of
the system. These new kinds of irritability and of sensibility in
consequence of new organization, appear from variety of facts in the more
mature animal; thus the formation of the testes, and consequent secretion
of the semen, occasion the passion of lust; the lungs must be previously
formed before their exertions to obtain fresh air can exist; the throat or
oesophagus must be formed previous to the sensation or appetites of hunger
and thirst; one of which seems to reside at the upper end, and the other at
the lower end of that canal.

Thus also the glans penis, when it is distended with blood, acquires a new
sensibility, and a new appetency. The same occurs to the nipples of the
breasts of female animals, when they are distended with blood, they acquire
the new appetency of giving milk. So inflamed tendons and membranes, and
even bones, acquire new sensations; and the parts of mutilated animals, as
of wounded snails, and polypi, and crabs, are reproduced; and at the same
time acquire sensations adapted to their situations. Thus when the head of
a snail is reproduced after decollation with a sharp rasor, those curious
telescopic eyes are also reproduced, and acquire their sensibility to
light, as well as their adapted muscles for retraction on the approach of
injury.

With every new change, therefore, of organic form, or addition of organic
parts, I suppose a new kind of irritability or of sensibility to be
produced; such varieties of irritability or of sensibility exist in our
adult state in the glands; every one of which is furnished with an
irritability, or a taste, or appetency, and a consequent mode of action
peculiar to itself.

In this manner I conceive the vessels of the jaws to produce those of the
teeth, those of the fingers to prod