320 EEV. J. T. GULICK ON 



similar environments undergo similar transformation ('Anniver- 

 sary Memoirs of the Boston Society of Natural History,' 1880 ; 

 " The Grenesis of tlie Tertiary Species of Planorlis at Steinheim," 

 pp. 24-29). 



In the description of these principles I have used the adjective 

 "Independent" to signify that the principle is operating in 

 sections of the species that are prevented from intergenerating. 

 If Isolated Selection were used instead of Independent Selection, 

 it would be constantly liable to be understood as meaning Selec- 

 tion acting upon sections produced simply by geographical sepa- 

 ration ; for Darwin never used Isolation to designate the pre- 

 vention of free crossing in other ways. In the term " Independent 

 Variation " Mr. Romanes has already used the adjective " In- 

 dependeoit^^ as meaning ^'^ when accompanied with the prevention 

 of intercrossing ; " and as it is less likely to be misunderstood, I 

 prefer it. Part of what Eomanes indicates by " Independent Va- 

 riation " is, I think, in my scheme distributed between the four 

 principles of Assirailational, Eliminatioual, Amalgamational, and 

 Fecundal Transformation when acting on independent groups. 

 As these principles are quite distinct, the separate names will be 

 a convenience. If there are other forms of transformation, the 

 causes of 'nbich cannot be given, I would prefer to class them as 

 due to unknown causes rather than attribute them to Variation, 

 which, as there used, is only a name for unexplained transforma- 

 tion. I would not turn Variation from its usual meaning, which 

 is deviation from the average character of an intergenerating 

 group. 



The Peevasive Influence of the Causes of Teansfoemation, 

 AND THE Law of Intension, 

 In my paper on " Divergent Evolution through Cumulative 

 Segregation," p. 215, I made the statement that, " When Sepa- 

 rate Generation is long continued, we have reason to believe, it 

 always passes into Segregate Generation with divergent evo- 

 lution." The same had been expressed in a previous paper by 

 the statement that " Variation is so strong, that all that is nei es- 

 sary to secure a divergence of types is to prevent their inter- 

 mingling "*. The certainty that Independent Generation with 

 transformation will never produce parallel, but always more or 



* "Diversity of Evolution under one Set of External Conditions," Journ. 

 Linn. Sot;., Zool. toI. xi. p. 499. 



