CHAPTER II. 

 THE EARLIER HISTORY OF ONTOGENY. 



Caspar Fkiedrich Wolff. 



The Evolution of Animals as known to Aristotle. — His Knowledge of the 

 Ontogeny of the Lower Animals. — Stationary Condition of the Scien- 

 tific Study of Nature during the Christian Middle Ages.— First Awaken- 

 ing of Ontogeny in the Beginning of the Seventeenth Century. — Fa- 

 bricius ab Aquapendente. — Harvey. — Marcello Malpighi. — Importance 

 of the Incubated Chick. — The Theories of Pre-formation and Encase- 

 ment (Evolution and Pre -delineation). — Theories of Male and Female 

 Encasement. — Either the Sperm-animal or the Egg as the Pre-formed 

 Individual. — Animalculists : Leeuwenhoek, Hartsoeker, Spallanzani. — 

 Ovulists : Haller, Leibnitz, Bonnet. — Victory of the Theory of Evolution 

 owing to the Authority of Haller and Leibnitz. — Caspar Friedrich Wolff. 

 — His Fate and Works. — The Theoria Generationis. — Ke-formation, or 

 Epigenesis. — The History of the Evolution of the Intestinal Canal. — 

 The Foundations of the Theory of Germ-layers (Four Layers, or Leaves). 

 — The Metamorphosis of Plants. — The Germs of the Cellular Theory. 

 —Wolff's Monistic Philosophy. 



" He who ^vishes to explain Generation must take for his thenae the 

 organic body and its constituent parts, and philosophize about them ; he 

 must show how these parts originated, and how they came to be in that rela- 

 tion in which they stand to each other. But he who learns to know a thing 

 aot only directly from its phenomena, but also its reasons and causes ; and 

 who, therefore, not by the phenomena merely, but by these also, is compelled 

 to say : ' The thing must be so, and it caimot be otherwise ; it is necessarily 

 of such a character ; it must have such qualities ; and it is impossible for 

 it to possess others' — understands the thing not only historically but 

 truly philosophically, and he has a philosophic knowledge of it. Our own 



