On the Origin of Species by Means of Natural Selection: Or, The Preservation of Favoured Races in the Struggle for LifeEaston Press, 1976 - 470 páginas |
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Página 243
... fertility of varieties , that is of the forms known or believed to be descended from common parents , when crossed , and likewise the fertility of their mongrel offspring , is , with reference to my theory , of equal importance with the ...
... fertility of varieties , that is of the forms known or believed to be descended from common parents , when crossed , and likewise the fertility of their mongrel offspring , is , with reference to my theory , of equal importance with the ...
Página 244
... fertility adduced by different hybridisers , or by the same observer from experiments made during different years . It can thus be shown that neither sterility nor fertility affords any certain distinction between species and varieties ...
... fertility adduced by different hybridisers , or by the same observer from experiments made during different years . It can thus be shown that neither sterility nor fertility affords any certain distinction between species and varieties ...
Página 249
... fertility , both of first crosses and of hybrids , graduates from zero to perfect fertility . It is surprising in how many curious ways this gradation can be shown ; but only the barest outline of the facts can here be given . When ...
... fertility , both of first crosses and of hybrids , graduates from zero to perfect fertility . It is surprising in how many curious ways this gradation can be shown ; but only the barest outline of the facts can here be given . When ...
Contenido
VARIATION UNDER NATURE | 30 |
STRUGGLE FOR EXISTENCE | 45 |
NATURAL SELECTION | 59 |
Derechos de autor | |
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Términos y frases comunes
accumulated adapted admit affinities allied species America ancient appear beak become bees believe belonging birds breeds cause cells characters climate closely allied colour common progenitor continuous crossed crustaceans degree developed difficulty distinct species divergence doubt effects eggs embryo existing exterminated extinct extremely facts favourable fertilised fertility flowers formation forms fossil Fritz Müller genera genus geological geological period gradations greater number groups of species habits Hence hybrids hybrids produced important increase individuals inhabitants inherited insects instance instincts intercrossing intermediate kind lamellæ larvæ less living male mammals manner marsupials migration modified descendants natural selection naturalists nearly nest occasionally offspring organisation organs Origin of Species parent peculiar perfect pigeons pistil plants pollen present preserved principle probably produced quadrupeds ranked reciprocal crosses remarked resemblance rudimentary seeds slight South America stamens sterility structure struggle successive supposed swimbladder theory variability variations varieties vary whilst whole wings young