CONTENTS OF VOL. II. 



CHAPTEE XVIII. 



ON THE ADVANTAGES AND DISADVANTAGES OF CHANGED 

 CONDITIONS OF LIFE: STEEILITY FROM VARIOUS CAUSES. 



ON THE GOOD DERIVED FROM SLIGHT CHANGES IN THE CONDITIONS OP LIFE — 

 STERILITY FROM CHANGED CONDITIONS, IN ANIMALS, IN THEIR NATIVE COUNTRY 

 AND IN MENAGERIES — MAMMALS, BIRDS, AND INSECTS — LOSS OF SECONDARY 

 SEXUAL CHARACTERS AND OF INSTINCTS — CAUSES OF STERILITY — STERILITY 

 OF DOMESTICATED ANIMALS FROM CHANGED CONDITIONS — SEXUAL INCOMPATI- 

 BILITY OP INDIVIDUAL ANIMALS — STERILITY OF PLANTS FROM CHANGED CONDI- 

 TIONS OF LIFE — CONTABESCENCE OF THE ANTHERS — MONSTROSITIES AS A CAUSE 

 OF STERILITY — DOUBLE FLOWERS — SEEDLESS FRUIT — STERILITY FROM THE 

 EXCESSIVE DEVELOPMENT OP THE ORGANS OP VEGETATION — FROM LONG-CONTINUED 

 PROPAGATION BY BUDS — INCIPIENT STERILITY THE PRIMARY CAUSE OP DOUBLE 

 FLOWERS AND SEEDLESS FRUIT Page 145 



CHAPTEE XIX. 



SUMMARY OF THE FOUR LAST CHAPTERS, WITH REMARKS 

 ON HYBRIDISM. 



ON THE EFFECTS OP CROSSING — THE INFLUENCE OF DOMESTICATION ON FERTILITY 

 — CLOSE INTERBREEDING — GOOD AND EVIL RESULTS FROM CHANGED CONDITIONS 

 OP LIFE — VARIETIES WHEN CROSSED NOT INVARIABLY FERTILE — ON THE DIF- 

 FERENCE IN FERTILITY BETWEEN CROSSED SPECIES AND VARIETIES — CONCLUSIONS 

 WITH RESPECT TO HYBRIDISM — LIGHT THROWN ON HYBRIDISM BY THE ILLEGITI- 

 MATE PROGENY OF DIMORPHIC AND TRIMORPHIC PLANTS — STERILITY OP CROSSED 

 SPECIES DUE TO DIFFERENCES CONFINED TO THE REPRODUCTIVE SYSTEM — NOT 

 ACCUMULATED THROUGH NATURAL SELECTION — REASONS WHY DOMESTIC VARIETIES 

 ARE NOT MUTUALLY STERILE — TOO MUCH STRESS HAS BEEN LAID ON THE 

 DIFFERENCE IN FERTILITY BETWEEN CROSSED SPECIES AND CROSSED VARIETIES — 

 CONCLUSION 173 



EVIL 



CHAPTEE XX. 



***** 



114 



SELECTION BY MAN. 



SELECTION A DIFFICULT ART — METHODICAL, UNCONSCIOUS, AND NATURAL SELECTION 

 RESULTS OP METHODICAL SELECTION — CARE TAKEN IN SELECTION — SELECTION 

 WITH PLANTS — SELECTION CARRIED ON BY THE ANCIENTS, AND BY SEMI-CIVILISED 

 PEOPLE — UNIMPORTANT CHARACTERS OFTEN ATTENDED TO — UNCONSCIOUS SELEC- 

 TION — AS CIRCUMSTANCES SLOWLY CHANGE, SO HAVE OUR DOMESTICATED ANIMALS 

 CHANGED THROUGH THE ACTION OF UNCONSCIOUS SELECTION — INFLUENCE OF 

 DIFFERENT BREEDERS ON THE SAME SUB-VARIETY — PLANTS AS AFFECTED BY 

 UNCONSCIOUS SELECTION — EFFECTS OF SELECTION AS SHOWN BY THE GREAT 

 AMOUNT OF DIFFERENCE IN THE PARTS MOST VALUED BY MAN 192 



