62 CALIFORNIA ACADEMY OF SCIENCES. 



II. Progressive. Produced by the action of environ- 

 ment upon the whole organism 

 or by the interaction of parts. 



1. Definite. Direct action of environment in 



one direction, including use and 

 disuse. 



2. Indefinite. General action of environment 



in producing variations which 

 can be accumulated by natural 

 selection. 

 Dr. W. K. Brooks in his book on heredity (p. 213) 



quotes the following secondary laws of variation which 



should be borne in mind: 



(1) " Specific characters are more variable than gen- 

 eric characters." (Darwin, Origin of Species, p. 122.) 



(2) lt Species of the larger genera in each country 

 vary more frequently than species of the smaller gen- 

 era." (1. c., p. 44.) 



(3) "A part developed in any species in an extra- 

 ordinary degree or manner, in comparison with the 

 same part in allied species, tends to be highly vari- 

 able." (1. c., p. 119.) 



(4) "If any given character is very variable in one 

 species of a group, it will tend to be variable in allied 

 species, and if any given character is perfectly constant 

 in one species of a group it will tend to be constant in 

 allied species." (Walsh, Proc. Ent. Soc. Phila., Oct. 

 1863, p. 213.) 



The above discussion has answered the question, is 

 natural selection creative? in the negative. An attempt 

 has been made to show that it is not even admissible to 

 assume unlimited variation as affording material for 

 natural selection. Prof. Schurman goes even a step 

 farther than this with regard to the origin of varia- 



