y differ, and thence produce parts not similar to the
father, but of a kind belonging in part to the mother; and thus, though the
original stamen or living ens was derived totally from the father, yet new
irritabilities or sensibilities being excited, a change of form
corresponding with them will be produced. Nor could the production of mules
exist, if the stamen or miniature of all the parts of the embryon is
previously formed in the male semen, and is only distended by nourishment
in the female uterus. Whereas this difficulty ceases, if the embryon be
supposed to consist of a living filament, which acquires or makes new parts
with new irritabilities, as it advances in its growth.

The form, solidity, and colour, of the particles of nutriment laid up for
the reception of the first living filament, as well as their peculiar kind
of stimulus, may contribute to produce a difference in the form, solidity,
and colour of the fetus, so as to resemble the mother, as it advances in
life. This also may especially happen during the first state of the
existence of the embryon, before it has acquired organs, which can change
these first nutritive particles, as explained in No. 5. 2. of this Section.
And as these nutritive particles are supposed to be similar to those, which
are formed for her own nutrition, it follows that the fetus should so far
resemble the mother.

This explains, why hereditary diseases may be derived either from the male
or female parent, as well as the peculiar form of either of their bodies.
Some of these hereditary diseases are simply owing to a deficient activity
of a part of the system, as of the absorbent vessels, which open into the
cells or cavities of the body, and thus occasion dropsies. Others are at
the same time owing to an increase of sensation, as in scrophula and
consumption; in these the obstruction of the fluids is first caused by the
inirritability of the vessels, and the inflammation and ulcers which
succeed, are caused by the consequent increase of sensation in the
obstructed part. Other hereditary diseases, as the epilepsy, and other
convulsions, consist in too great voluntary exertions in consequence of
disagreeable sensation in some particular diseased part. Now as the pains,
which occasion these convulsions, are owing to defect of the action of the
diseased part, as shewn in Sect. XXXIV. it is plain, that all these
hereditary diseases may have their origin either from defective
irritabi