40 THE EVOLUTION OF MAN. 



other species, pre-existed in the semen ; that they existed 

 in the ancestors as far back as Adam, therefore since the 

 beginning of things, always in the form of organized bodies." 



The Theory of Encasement seemed to receive its most 

 important experimental support in the researches of Bonnet, 

 one of its most zealous adherents. He observed, for the 

 first time, in Plant-lice, the so-called " virginal generation," 

 or parthenogenesis, which is an interesting form of propaga- 

 tion lately proved by Siebold and others, in many other 

 articulated animals, such as various Crabs and Insects.^^ 

 The females of these and other lower animals of certain 

 groups propagate for several generations without having 

 been impregnated by a male. Such eggs, which for their 

 evolution do not require to be impregnated, are called 

 " false eggs," Pseudova, or Spores. Bonnet, in 1745, for the 

 first time observed that a female Plant-louse, which he had 

 completely shut off, as in a nunnery, and shielded from all 

 contact with males, after shedding its skin four times, gave 

 birth on the eleventh day to a living female, and within 

 the next twenty days produced as many as ninety-four 

 other females ; and that soon all of these, without having 

 come in contact with a male, multiplied again in the same 

 virgin manner. Thereupon, of course, it seemed that a 

 tangible proof of the truth of the Theory of Encasement, 

 according to the interpretation of Ovulists, had been 

 abundantly furnished, and it naturally became almost uni- 

 versally accepted in this sense. 



The case stood thus, when suddenly, in the year 1759, 

 Caspar Friedrich Wolff, then a young man, appeared, and 

 with his new Theory of Epigenesis gave the death-blow to 

 the entire Theory of Pre-formation. Wolff was born at 



