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 35
... insects which are cha- racterised as varieties in Mr. Wollaston's admirable work , but which would certainly be ranked as distinct species by many entomologists . Even Ireland has a few animals , now generally regarded as varieties ...
... insects which are cha- racterised as varieties in Mr. Wollaston's admirable work , but which would certainly be ranked as distinct species by many entomologists . Even Ireland has a few animals , now generally regarded as varieties ...
Página 36
... insects found living on different plants , have been observed by Mr. Walsh to present in their larval or mature state , or in both states , slight , though constant differences in colour , size , or in the nature of their secretions ...
... insects found living on different plants , have been observed by Mr. Walsh to present in their larval or mature state , or in both states , slight , though constant differences in colour , size , or in the nature of their secretions ...
Página 41
... insects of two districts , into two nearly equal masses , the species of the larger 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 ...
... insects of two districts , into two nearly equal masses , the species of the larger 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 ...
Página 42
... insects , that in large genera the amount of difference between the species is often exceedingly small . I have endeavoured to test this numerically by averages , and , as far as my imperfect results go , they confirm the view . I have ...
... insects , that in large genera the amount of difference between the species is often exceedingly small . I have endeavoured to test this numerically by averages , and , as far as my imperfect results go , they confirm the view . I have ...
Página 46
... insects or seeds , and are thus constantly destroying life ; or we forget how largely these songsters , or their eggs , or their nestlings , are destroyed by birds and beasts of prey ; we do not always bear in mind , that , though food ...
... insects or seeds , and are thus constantly destroying life ; or we forget how largely these songsters , or their eggs , or their nestlings , are destroyed by birds and beasts of prey ; we do not always bear in mind , that , though food ...
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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