LECTURE II 



Summary Experimental Evolution based on Three Groups of Facts 

 First Group : the Facts of Natural or Spontaneous Variation : 

 Organisms are not rigid structures, but exhibit much plasticity. 

 Facts of Variation in Colour, correlated sometimes, and 

 perhaps always, with variation of chemical composition 

 (Armand Gautier's investigations) ; Variation in Dimensions and 

 Experiments on the real cause of this Variation, .Semper and the 

 Author ; Variation in Integuments, Form, Shape of Fruits and 

 Leaves, Flowers Penzig's Pflanzcn-Ter dialogic Skeleton, 

 Muscles, Internal Organs and Viscera ; Sexuality Camerano's 

 Neotenia. 



TJIUI.I groups of facts lie at the basis of experi- 

 mental transformism and display at the same time 

 its conditions and its methods. The first, and most 

 important, comprises the facts which illustrate varia- 

 bility in the state of nature, natural or spontaneous 

 variability. Spontaneous, we call it, but in fact we use 

 the word only because we are ignorant of the real and 

 positive causes of this variability. The second group 

 includes the facts of variation under domestication 

 and culture ; the third, the facts illustrating the direct 

 influence of environment as a factor of modification and 

 transformation. These three groups of facts require 



