entury, and there is reason, then, for Digby's attack upon Aristotelian
ideas of form and matter and of the persistence of "qualities" in
physics and "faculties" in biology.

Expressing his disdain of word-spinning, Digby attempts to explain all
phenomena by two "virtues" only, rarity and density working by local
motion. In discussing embryonic development, Digby writes, "...our
maine question shall be, Whether they be framed entirely at once; or
successively, one part after another? And, if this later way, which
part first?"[3] Toward this end, Digby makes some direct observations
upon the development of the chick embryo, incubating the eggs so that
the "creatures ... might be continually in our power to observe in them
the course of nature every day and houre."[4] His description of chick
development is of epigenetic bent:

...you may lay severall egges to hatch; and by breaking them at
severall ages you may distinctly observe every hourely mutation in
them, if you please. The first will bee, that on one side you shall
find a great resplendent clearnesse in the white. After a while, a
little spott of red matter like bload, will appeare in the middest
of that clearnesse fastened to the yolke: which will have a motion
of opening and shutting; so as sometimes you will see it, and
straight againe it will vanish from your sight; and indeede att the
first it is so litle, that you can not see it, but by the motion of
it; for att every pulse, as it openeth, you may see it, and
immediately againe, it shutteth in such sort, as it is not to be
discerned. From this red specke, after a while there will streame
out, a number of litle (almost imperceptible) red veines. Att the
end of some of which, in time there will be gathered together, a
knotte of matter which by litle and litle, will take the forme of a
head; and you will ere long beginne to discerne eyes and a beake in
it. All this while the first red spott of blood, groweth bigger and
solider; till att the length, it becometh a fleshy substance; and
by its figure, may easily be discerned to be the hart: which as yet
hath no other enclosure but the substance of the egge. But by litle
and litle the rest of the body of an animal is framed out of those
red veines which streame out all aboute from the hart. And in
processe of time, that body incloseth the hart within i