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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... animals which unite for each birth and wander much , and which do not breed at a very quick rate . Hence with animals of this nature , for instance birds , varieties will generally be confined to separated countries ; and this I find to ...
... animals which unite for each birth and wander much , and which do not breed at a very quick rate . Hence with animals of this nature , for instance birds , varieties will generally be confined to separated countries ; and this I find to ...
131 페이지
... animal , and as eyes are certainly not necessary to animals having subterranean habits , a reduction in their size , with the adhesion of the eyelids and growth of fur over them , might in such case be an advantage ; and if so , natural ...
... animal , and as eyes are certainly not necessary to animals having subterranean habits , a reduction in their size , with the adhesion of the eyelids and growth of fur over them , might in such case be an advantage ; and if so , natural ...
134 페이지
... animals , several authentic instances could be adduced of species having largely extended , within historical times , their range from warmer to colder latitudes , and conversely ; but we do not posi- tively know that these animals were ...
... animals , several authentic instances could be adduced of species having largely extended , within historical times , their range from warmer to colder latitudes , and conversely ; but we do not posi- tively know that these animals were ...
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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