34 THE EVOLUTION OF MAN. 



of animals and plants received so great an impulse from 

 Linnseus' famous Systema NaturcB, the History of Evolution 

 made scarcely any progress. It v/as in the year 1759 that 

 Caspar Friedrich Wolff made his appearance, and his genius 

 gave an entirely new direction to this science. Until then 

 Embryology was almost exclusively occupied in unsuccessful 

 attempts to construct various theories of evolution from the 

 scanty material already acquired. 



The theory which at that time gained almost universal 

 acceptance, and which continued to be generally received 

 during the entire eighteenth century, is in Germany com- 

 monly called the Theory of Unfolding (Auswickelung), or 

 Evolution, but is better spoken of as the Theory of Pre- 

 formation.^'^ Its main idea is the following : no really new 

 formation takes place during the evolution of each indi- 

 vidual organism, animal or plant, including therefore Man ; 

 there is only a growth and an unfolding of parts, all 

 of which have, from eternity, been present, pre-formed, and 

 complete, though only very minute, and wrapped together. 

 Every organic germ, therefore, contains all the parts and 

 organs of the body pre-formed and represented in their 

 subsequent form, position, and connection, and the entire 

 course of the evolution of the individual, the entire onto- 

 genetic process, is nothing but an evolution in the most 

 exact meaning of the word ; namely, an unwrapping of 

 wrapped-up parts already formed. Hence, for example, in 

 a hen's Qgg we do not find a simple cell which undergoes 

 division, and the generation of cells of which form layers of 

 germs, and by various changes, separations, and new for- 

 mations, ultimately bring into being the body of the Bird ; 

 but every hen's egg contains from the beginning a complete 



