The Origin of Species by Means of Natural Selection,: Or the Preservation of Favoured Races in the Struggle for LifeJohn Murray, Albemarle Street., 1891 - 432 páginas |
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Página 220
... sterility of species when first crossed , and the sterility of the hybrids produced from them . Pure species have of course their organs of reproduction in a perfect condition , yet when intercrossed they produce either few or no ...
... sterility of species when first crossed , and the sterility of the hybrids produced from them . Pure species have of course their organs of reproduction in a perfect condition , yet when intercrossed they produce either few or no ...
Página 221
... 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 for all practical ...
... 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 for all practical ...
Página 222
... sterility between distinct species is a universal law of nature . He experimented on some of the very same species as did Gärtner . The difference in their results may , I think , be in part accounted for by Herbert's great ...
... sterility between distinct species is a universal law of nature . He experimented on some of the very same species as did Gärtner . The difference in their results may , I think , be in part accounted for by Herbert's great ...
Página 223
... of close interbreeding is thus prevented . Any one may readily convince himself of the efficiency of insect - agency by examining the flowers of the more sterile kinds of hybrid. CHAP . IX . ] 223 DEGREES OF STERILITY .
... of close interbreeding is thus prevented . Any one may readily convince himself of the efficiency of insect - agency by examining the flowers of the more sterile kinds of hybrid. CHAP . IX . ] 223 DEGREES OF STERILITY .
Página 226
... sterility we have self - fertilised hybrids producing a greater and greater number of seeds up to perfect fertility . The hybrids raised from two species which are very difficult to cross , and which rarely produce any offspring , are ...
... sterility we have self - fertilised hybrids producing a greater and greater number of seeds up to perfect fertility . The hybrids raised from two species which are very difficult to cross , and which rarely produce any offspring , are ...
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Términos y frases comunes
accumulated adapted admit affinities allied species America analogous ancient appear beak become bees believe belonging birds breeds cause cells characters climate closely allied colour continued crossed crustaceans degree developed difficulty distinct species domestic animals doubt effects eggs embryo existing extinct extremely facts favourable female fertilised fertility flowers formation formerly forms fossil Fritz Müller genera genus geological geological period Glacial period gradations greater number habits Hence hybrids 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 occur oceanic islands offspring organisation organs parent peculiar perfect pigeon pistil pollen present preserved principle probably produced quadrupeds ranked reciprocal crosses remarked resemblance rudimentary seeds sexual selection Silurian slight South America stamens sterility structure successive supposed tend theory tion variability variations varieties vary whilst whole wings young