402 



INDEX. 



give it opportunity to do its 

 work, 54 ; hindering rather 

 than promoting species change, 

 56 ; Korschinsky's radical posi- 

 tion against, 91 ; may produce 

 continuous change, but not dis- 

 continuous series of species, 

 73 ; Morgan's antagonism of 

 species-forming by, 93 ; natu- 

 ral, defined, 13; natural, needs 

 sexual selection theory for 

 support, 125 ; natural, rests too 

 largely on analogy with arti- 

 ficial selection, 150; needs the 

 support of the sexual selection 

 theory, 85 ; not able to explain 

 complex adaptation, 144 ; not 

 able to explain degeneration, 

 146 ; not able to explain over- 

 specialisation, 146; not able 

 to produce many-branched de- 

 scent and discontinuity in 

 series, 142; objection to, based 

 on the linear and quantitative 

 character of fluctuating varia- 

 tions, 70; objections to based 

 on over-specialisation, 53 ; per- 

 sonal, how real, 82 ; Pfeffer's 

 objection, based on the small- 

 ness of species change, 75 ; 

 rests too largely on an analogy 

 with artificial selection, 86; 

 rigour of. questioned, 148; 

 theories, Wigand's criticism 

 of, 387 ; theory of, dis- 

 tinguished from theory of de- 

 scent, 17 



Selection, germinal, objection to 

 theory of. 200 ; germinal, Weis- 

 mann's theory of, 188, 193 ; 

 germinal, resulting in deter- 

 minate variation, 198 



Selection, mechanical, 246 



Selection, ontogenetic, 208 



Selection, organic, 208; organic, 

 Delage and Plate's criticisms 

 of, 210 



Selection, physiological, criti- 

 cisms of, 247 



Selection, reproductive, Pear- 

 son's theory of, 249 



Selection, sexual, 106, 120; al- 

 ternative explanations of, 124; 

 answers to objections to, 148; 

 criticism of, by Wolff, G., 126; 



criticism of theory of, 113; 

 Darwin's basis of theory, 112; 

 defined, 16; Morgan's objec- 

 tions to, 118; other theories to 

 replace theory of, 123; refer- 

 ences to discussions of, 125 

 Selectionists, concessions of, 90 

 Sexual differences, classification 

 of secondary, 107 ; secondary, 

 106; significance of, no 

 Snodgrass, R. E., studies on bills 

 of Galapagos birds, 323 ; 

 studies on biologic selection, 



245 



Sociology, relations to biology, 

 references for, 24 ; relation to 

 theory of descent, 21 



Species-forming, causes and 

 means of segregation the chief 

 factors in, 377 ; determinate 

 variation as a factor, 33 ; de 

 Vries's discussion of, by selec- 

 tion, 389; Loeb's attitude to- 

 ward the problem of, 393 ; on 

 a basis of fluctuating varia- 

 tion, 35; theories of, 187; 

 Tower's experiments and con- 

 clusions, 309, 394 



Spencer, H., example of the 

 femur of the whale, 38; pic- 

 ture of the inutility of ad- 

 vantage in a single direction, 

 48; theory of ultimate struct- 

 ure of protoplasm, 216 



Sport in cattle, recent example 



of, 358 

 Sterility, inter-species, difficulty 



of explaining by selection, 76 

 Struggle for existence, actual 



rigour of, 79; defined, 13 

 Symbiosis of hermit crab and 



polyp, 23 



Tayler, J. L., answer to objec- 

 tion to selection based on 

 linear variation, 141 ; Darwin- 

 ian explanation of degenera- 

 tion, 147; explanation of de- 

 generation by natural selec- 

 tion, 162; general defence of 

 natural selection, 153 



Theology, relation of, to theory 

 of descent, 20 



Tower, W. L., experiments and 



