The Origin of Species by Means of Natural Selection,: Or the Preservation of Favoured Races in the Struggle for LifeAppleton, 1898 - 432 páginas |
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Página 19
... sterility of hybrids , which have their reproductive organs in an imperfect con- dition , is a different case from the difficulty of uniting two pure species , which have their reproductive organs perfect ; yet these two distinct ...
... sterility of hybrids , which have their reproductive organs in an imperfect con- dition , is a different case from the difficulty of uniting two pure species , which have their reproductive organs perfect ; yet these two distinct ...
Página 20
... Sterility of first Crosses and of Hybrids . At one time it appeared to me probable , as it has to others , that the sterility of first crosses and of hybrids might have been slowly acquired through the natural selection of slightly ...
... Sterility of first Crosses and of Hybrids . At one time it appeared to me probable , as it has to others , that the sterility of first crosses and of hybrids might have been slowly acquired through the natural selection of slightly ...
Página 21
... sterility with other species would follow as a necessary contingency . In the second place , it is almost as much opposed to the theory of natural selection as to that of special creation , that in reciprocal crosses the male element of ...
... sterility with other species would follow as a necessary contingency . In the second place , it is almost as much opposed to the theory of natural selection as to that of special creation , that in reciprocal crosses the male element of ...
Página 22
... sterility ? Yet an advance of this kind , if the theory of natural selection be brought to bear , must have incessantly occurred with many species , for a multitude are mutually quite barren . With sterile neuter insects we have reason ...
... sterility ? Yet an advance of this kind , if the theory of natural selection be brought to bear , must have incessantly occurred with many species , for a multitude are mutually quite barren . With sterile neuter insects we have reason ...
Página 23
... sterility in first crosses and in hybrids . In the case of first crosses , the greater or less difficulty in effecting an union and in obtaining offspring apparently depends on several distinct causes . There must sometimes be a ...
... sterility in first crosses and in hybrids . In the case of first crosses , the greater or less difficulty in effecting an union and in obtaining offspring apparently depends on several distinct causes . There must sometimes be a ...
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Términos y frases comunes
admit affinity allied species ancient animals appear Archipelago arctic areas become believe birds Cambrian changes characters cies classification climate closely allied common progenitor 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 individuals 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 parent parent-form peculiar perfect pistil plants pollen present probably produced quadrupeds reciprocal crosses regions remains remarked reproductive resemblance rocks rudimentary organs sediment seeds Silurian South America stage stamens sterility structure successive suppose terrestrial tertiary theory tion variations varieties whilst widely different wings