The Origin of Species by Means of Natural Selection: Or, The Preservation of Favored Races in the Struggle for Life, Volumen2D. Appleton, 1898 |
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Página 17
... appear to me clearly to indicate that the sterility both of first crosses and of hybrids is simply incidental or dependent on unknown differences in their reproductive systems ; the differences being of so peculiar and lim- ited a ...
... appear to me clearly to indicate that the sterility both of first crosses and of hybrids is simply incidental or dependent on unknown differences in their reproductive systems ; the differences being of so peculiar and lim- ited a ...
Página 33
... appears at first sight exactly the reverse of what occurs , in the ordinary unions of the individuals of the same species and with crosses between distinct species . It is , however , doubt- ful whether this is really so ; but I will ...
... appears at first sight exactly the reverse of what occurs , in the ordinary unions of the individuals of the same species and with crosses between distinct species . It is , however , doubt- ful whether this is really so ; but I will ...
Página 36
... appears to me , why domestic varieties have not become mutually infertile when crossed , but why this has so generally occurred with natural varieties , as soon as they have been permanently modified in a sufficient degree to take rank ...
... appears to me , why domestic varieties have not become mutually infertile when crossed , but why this has so generally occurred with natural varieties , as soon as they have been permanently modified in a sufficient degree to take rank ...
Página 65
... appear to be , if all the sedimentary . beds were removed which rest unconformably on them , and which could not have formed part of the original mantle under which they were crystallized . Hence it is probable that in some parts of the ...
... appear to be , if all the sedimentary . beds were removed which rest unconformably on them , and which could not have formed part of the original mantle under which they were crystallized . Hence it is probable that in some parts of the ...
Página 66
... difficulties , as it seems to me , prevent us from coming to any just conclusion on this head . When we see a species first appearing in the middle of any formation , it would. 66 ABSENCE OF INTERMEDIATE VARIETIES [ CHAP . X.
... difficulties , as it seems to me , prevent us from coming to any just conclusion on this head . When we see a species first appearing in the middle of any formation , it would. 66 ABSENCE OF INTERMEDIATE VARIETIES [ CHAP . X.
Otras ediciones - Ver todas
The Origin of Species by Means of Natural Selection: Or the ..., Volumen2 Darwin Vista completa - 1889 |
On the Origin of Species by Means of Natural Selection Charles Darwin Sin vista previa disponible - 2016 |
Términos y frases comunes
admit affinity allied species ancient animals appear Archipelago arctic areas become believe belonging birds Cambrian changes characters cies classification climate closely allied continent crustaceans degree deposited difficulty distant distinct species domestic doubt embryo eral Europe existing extinct fact faunas fertilised fertility flowers formations formerly forms fossil fresh-water Fritz Müller Gärtner genera genus geological period geological record Glacial period groups of species habits hybrids hybrids produced important inhabitants inherited insects instance intermediate intervals land larvæ less living mammals manner marine Marsupials migration modified descendants mongrels mountains natural selection naturalists nearly occur oceanic islands offspring organisation palæontologists Palæozoic parent parent-form peculiar perfect pistil plants pollen present probably produced quadrupeds reciprocal crosses regions remains remarked reproductive resemblance rocks rudimentary organs seeds Silurian South America stage stamens sterility structure successive suppose terrestrial tertiary theory tion variations varieties whilst whole widely different wings