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 28
... less sterile ; and we know that a cross between two forms , that have become widely or specifically different , produce hybrids which are almost always in some degree sterile . I am fully persuaded that this double parallelism is by no ...
... less sterile ; and we know that a cross between two forms , that have become widely or specifically different , produce hybrids which are almost always in some degree sterile . I am fully persuaded that this double parallelism is by no ...
Página 29
... less infertile . With trimor- phic species six unions are legitimate , or fully fer- tile , and twelve are illegitimate , or more or less infer- tile . The infertility which may be observed in various dimorphic and CHAP . IX ...
... less infertile . With trimor- phic species six unions are legitimate , or fully fer- tile , and twelve are illegitimate , or more or less infer- tile . The infertility which may be observed in various dimorphic and CHAP . IX ...
Página 30
... less favourable , so I have found it with illegitimate unions . It is well known that if pollen of a distinct species be placed on the stigma of a flower , and its own pollen be afterwards , even after a considerable interval of time ...
... less favourable , so I have found it with illegitimate unions . It is well known that if pollen of a distinct species be placed on the stigma of a flower , and its own pollen be afterwards , even after a considerable interval of time ...
Página 35
... less remarkable . In the first place , it may be observed that the amount of external difference between two species is no sure guide to their degree of mutual steril- ity , so that similar differences in the case of varieties would be ...
... less remarkable . In the first place , it may be observed that the amount of external difference between two species is no sure guide to their degree of mutual steril- ity , so that similar differences in the case of varieties would be ...
Página 37
... crossed three varieties of gourd , which like the maize has separated sexes , and he asserts that their mutual fertilisation is by so much the less easy as their differences are greater . How far CHAP . IX . ] 37 WHEN CROSSED .
... crossed three varieties of gourd , which like the maize has separated sexes , and he asserts that their mutual fertilisation is by so much the less easy as their differences are greater . How far CHAP . IX . ] 37 WHEN CROSSED .
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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