e the
two contradictory theories which in the eighteenth century kept their
adherents sharply divided, the theories of the ovulists and those of
the animalculists, and the dispute seemed to offer little hope of a
possible decision. The names of famous scientists and philosophers
were associated with these dissensions, those, for instance, of
Spallanzani and of Liebnitz, who applied the principles of generation
even to the soul. "Thus I should think," said Liebnitz, "that the
souls which will one day become human souls, were present in the germ;
that they have always existed as organized bodies in their progenitors
from Adam onwards--that is, from the beginning of things." [8]

Haller, the ovulist, who had great authority as a physiologist, in a
famous work, _Elementa physiologiae_, upheld the principle vigorously:
"_Nulla est epigenesis. Nulla in corpore animale pars ante aliam facta
est et omnes simul creatae existunt_" (nothing is created anew, no
part of the human body is made before any other part, all are created
at the same time). Making a calculation based on Biblical cosmogony of
the number of human beings who were packed in the ovaries of Eve, he
reckons them at two hundred thousand millions. Such was the state of
thought when in 1759 K. F. Wolff published some of his studies in the
work _Theoria generationis_, where he maintained, on the strength of
experiments and microscopic observations made on the embryos of fowls,
that new organisms are not pre-formed, but that they create themselves
entirely, starting from nothing--that is, from a microscopic cell,
simple as are all primitive cells. He described the simple process by
which the real evolution of individuals is brought about: from a
single cell, by division, two, and then four and then eight, are
formed, and so on. And the cells thus germinated divide themselves
into two or three tiny folds of "primitive folioles" from which all
the organs are evolved, beginning with the alimentary canal. "This
assertion," says Wolff "is not a fanciful theory; it is a description
of facts collected by means of the most trustworthy observations."

[Footnote 8: From Haeckel's _Anthropogenie_.]

All the scientists of his day knew and made use of the microscope; all
might have taken an egg, that is, the embryo of a fowl, as a subject
for observation; they were not indifferent to the problem of
individual genesis, but in their case it had merely excited the most
complex effo