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 2
... hand , have their reproductive organs functionally impotent , as may be clearly seen in the state of the male element in both plants and animals ; though the formative organs themselves are perfect in structure , as far as the ...
... hand , have their reproductive organs functionally impotent , as may be clearly seen in the state of the male element in both plants and animals ; though the formative organs themselves are perfect in structure , as far as the ...
Página 4
... hand , that the sterility of various species when crossed is so different in degree and graduates away so insensibly , and , on the other hand , that the fertility of pure species is so easily affected by various circumstances , that ...
... hand , that the sterility of various species when crossed is so different in degree and graduates away so insensibly , and , on the other hand , that the fertility of pure species is so easily affected by various circumstances , that ...
Página 5
... hand that an occasional cross with a dis- tinct individual or variety increases the vigour and fer- tility of the offspring , and on the other hand that very close interbreeding lessens their vigour and fertility , that I cannot doubt ...
... hand that an occasional cross with a dis- tinct individual or variety increases the vigour and fer- tility of the offspring , and on the other hand that very close interbreeding lessens their vigour and fertility , that I cannot doubt ...
Página 13
... hand , by very closely allied species generally uniting with facility . But the correspondence between syste- matic affinity and the facility of crossing is by no means strict . A multitude of cases could be given of very closely allied ...
... hand , by very closely allied species generally uniting with facility . But the correspondence between syste- matic affinity and the facility of crossing is by no means strict . A multitude of cases could be given of very closely allied ...
Página 17
... hand , 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 ...
... hand , 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 ...
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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