CHAPTER II. 



THE EARLIER HISTORY OF ONTOGEKY. 



CASPAR FRIEDRICH WOLFF. 



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

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

 tific Stndy 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-fonnation 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 Oenerationis. Ee-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 wishes to explain Generation must take for his theme 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 

 not 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 cannot 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 



