like the alimentary system, developed out of simple leaf-shaped
structures. Hence, Wolff came to the view by 1768 which Pander
developed in the Theory of Germinal Layers fifty years afterwards. His
principles are not literally correct; but he comes as near to the
truth in them as was possible at that time, and could be expected of
him.

Our admiration of this gifted genius increases when we find that he
was also the precursor of Goethe in regard to the metamorphosis of
plants and of the famous cellular theory. Wolff had, as Huxley showed,
a clear presentiment of this cardinal theory, since he recognised
small microscopic globules as the elementary parts out of which the
germinal layers arose.

Finally, I must invite special attention to the MECHANICAL character
of the profound philosophic reflections which Wolff always added to
his remarkable observations. He was a great monistic philosopher, in
the best meaning of the word. It is unfortunate that his philosophic
discoveries were ignored as completely as his observations for more
than half a century. We must be all the more careful to emphasise the
fact of their clear monistic tendency.


CHAPTER 1.3. MODERN EMBRYOLOGY.

We may distinguish three chief periods in the growth of our science of
human embryology. The first has been considered in the preceding
chapter; it embraces the whole of the preparatory period of research,
and extends from Aristotle to Caspar Friedrich Wolff, or to the year
1759, in which the epoch-making Theoria generationis was published.