manifest,
that those monstrous births, which consist in some deficiencies only, or
some redundancies of parts, originate from the deficiency or redundance of
the first nutriment prepared in the ovary, or in the part of the egg
immediately surrounding the cicatricula, as described above; and which
continues some time to excite the first living filament into action, after
the simple animal is completed; or ceases to excite it, before the complete
form is accomplished. The former of these circumstances is evinced by the
eggs with double yolks, which frequently happen to our domesticated
poultry, and which, I believe, are so formed before impregnation, but which
would be well worth attending to, both before and after impregnation; as it
is probable, something valuable on this subject might be learnt from them.
The latter circumstance, or that of deficiency of original nutriment, may
be deduced from reverse analogy.

There are, however, other kinds of monstrous births, which neither depend
on deficiency of parts, or supernumerary ones; nor are owing to the
conjunction of animals of different species; but which appear to be new
conformations, or new dispositions of parts in respect to each other, and
which, like the variation of colours and forms of our domesticated animals,
and probably the sexual parts of all animals, may depend on the imagination
of the male parent, which we now come to consider.

VI. 1. The nice actions of the extremities of our various glands are
exhibited in their various productions, which are believed to be made by
the gland, and not previously to exist as such in the blood.

Thus the glands, which constitute the liver, make bile; those of the
stomach make gastric acid; those beneath the jaw, saliva; those of the
ears, ear-wax; and the like. Every kind of gland must possess a peculiar
irritability, and probably a sensibility, at the early state of its
existence; and must be furnished with a nerve of sense, or of motion, to
perceive, and to select, and to combine the particles, which compose the
fluid it secretes. And this nerve of sense which perceives the different
articles which compose the blood, must at least be conceived to be as fine
and subtile an organ, as the optic or auditory nerve, which perceive light
or sound. See Sect. XIV. 9.

But in nothing is this nice action of the extremities of the blood-vessels
so wonderful, as in the production of contagious matter. A small drop of
variolous c