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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53 페이지
... genera on one side , and those of the smaller genera on the other side , and it has invariably proved to be the case that a larger proportion of the species on the side of the larger genera presented varieties , than on the side of the ...
... genera on one side , and those of the smaller genera on the other side , and it has invariably proved to be the case that a larger proportion of the species on the side of the larger genera presented varieties , than on the side of the ...
369 페이지
... genera , each with the same number of species , then we may conclude that generally only one species of each of the older genera has left modified descendants , which constitute the new genera containing the several species ; the other ...
... genera , each with the same number of species , then we may conclude that generally only one species of each of the older genera has left modified descendants , which constitute the new genera containing the several species ; the other ...
429 페이지
... genera on the right hand , which diverged from a com- mon parent at the fifth stage of descent . These five genera have also much in common , though less than when grouped in subfamilies ; and they form a family distinct from that ...
... genera on the right hand , which diverged from a com- mon parent at the fifth stage of descent . These five genera have also much in common , though less than when grouped in subfamilies ; and they form a family distinct from that ...
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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 divergence domestic doubt effects eggs embryo existing extinct extremely facts favorable fertility flowers formation forms fossil Fritz Müller genera genus geological geological period Glacial period gradations greater number groups of species habits Hence hybrids hybrids produced important individuals inhabitants inherited insects instance instincts intercrossing intermediate intervals kind lamellæ larvæ less living male mammals manner marsupials migration modified descendants natural selection naturalists nearly nest occasionally 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