The Origin of Species by Means of Natural Selection; Or, the Preservation of Favored Races in the Struggle for Life ...A.L. Burt, 1890 - 538페이지 |
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... crossed a barb with a spot , which is a white bird with a red tail and red spot on the forehead , and which notoriously breeds very true ; the mongrels were dusky and mottled . I then crossed one of the mongrel barb - fantails with a ...
... crossed a barb with a spot , which is a white bird with a red tail and red spot on the forehead , and which notoriously breeds very true ; the mongrels were dusky and mottled . I then crossed one of the mongrel barb - fantails with a ...
305 페이지
... crossed with the Nico- tiana glutinosa , always yielded hybrids not so sterile as those which were produced from the four other varieties when crossed with N. glutinosa . Hence , the reproductive system of this one variety must have ...
... crossed with the Nico- tiana glutinosa , always yielded hybrids not so sterile as those which were produced from the four other varieties when crossed with N. glutinosa . Hence , the reproductive system of this one variety must have ...
307 페이지
... crossed with a third species , the hybrids are widely different from each other ; whereas if two very distinct varieties of one species are crossed with another species , the hybrids do not differ much . But this conclusion , as far as ...
... crossed with a third species , the hybrids are widely different from each other ; whereas if two very distinct varieties of one species are crossed with another species , the hybrids do not differ much . But this conclusion , as far as ...
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adapted admit affinities allied species America ancient appear Asa Gray beak become bees believe belonging birds breeds cause cells characters climate closely allied color continued crossed crustaceans degree developed difficulty distinct species domestic doubt effects eggs embryo existing extinct extremely facts favorable females fertility flowers formation forms fossil Fritz Müller genera genus geological geological period gilt top Glacial period gradations greater number groups of species habits Hence hybrids hybrids produced important 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 oceanic islands offspring organs parent peculiar perfect pigeons pistil pollen present principle probably produced quadrupeds ranked remarked resemblance rudimentary seeds sexual selection Silurian slight South America stamens sterility structure successive suppose tend theory tion variability variations varieties vary whole widely different wings young