The Origin of Species by Means of Natural Selection: Or the Preservation of Favored Races in the Struggle for LifeD. Appleton, 1904 - 435 páginas |
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Página 23
... crossing of a few aboriginal species ; but by crossing we can only get forms in some degree intermediate between ... crossed one with another for several genera- tions , hardly two of them are alike , and then the diffi- culty of the ...
... crossing of a few aboriginal species ; but by crossing we can only get forms in some degree intermediate between ... crossed one with another for several genera- tions , hardly two of them are alike , and then the diffi- culty of the ...
Página 26
... crossing of any lesser number : how , for instance , could a pouter be produced by crossing two breeds unless one of the parent - stocks possessed the characteristic enormous crop ? The supposed aboriginal stocks must . all have been ...
... crossing of any lesser number : how , for instance , could a pouter be produced by crossing two breeds unless one of the parent - stocks possessed the characteristic enormous crop ? The supposed aboriginal stocks must . all have been ...
Página 28
... crossed , none of which are blue or have any of the above - specified marks , the mongrel offspring are very apt suddenly to acquire these characters . To give one instance out of several which I have ob- served : I crossed some white ...
... crossed , none of which are blue or have any of the above - specified marks , the mongrel offspring are very apt suddenly to acquire these characters . To give one instance out of several which I have ob- served : I crossed some white ...
Página 29
... crossed by the rock - pigeon : I say within a dozen or twenty generations , for no instance is known of crossed descendants reverting to an ancestor of foreign blood , removed by a greater number of generations . In a breed which has ...
... crossed by the rock - pigeon : I say within a dozen or twenty generations , for no instance is known of crossed descendants reverting to an ancestor of foreign blood , removed by a greater number of generations . In a breed which has ...
Página 30
... appearance of the blue colour and various black marks in all the breeds , both when kept pure and when crossed ; -and lastly , the mongrel offspring being perfectly fertile ; -from these several reasons 30 [ CHAP . I. DOMESTIC PIGEONS .
... appearance of the blue colour and various black marks in all the breeds , both when kept pure and when crossed ; -and lastly , the mongrel offspring being perfectly fertile ; -from these several reasons 30 [ CHAP . I. DOMESTIC PIGEONS .
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Términos y frases comunes
adapted affinities allied species America ancient appear Asa Gray beak become bees believe belonging birds breeds cause cells characters climate closely allied colour common continent crossed crustaceans degree developed difficulty distinct species domestic doubt effects eggs embryo existing extinct extremely facts favourable fertilised fertility flowers formation forms fossil Fritz Müller genera genus geological geological period Glacial period gradations greater number groups of species habits Hence hybrids important individuals inhabitants inherited insects instance instincts intercrossing intermediate kind lamellæ larvæ less living males mammals manner marsupials migration modified descendants natural selection naturalists nearly nest occasionally offspring organisation organs parent peculiar perfect pigeon pistil pollen present principle probably produced progenitor quadrupeds ranked remarked resemblance rudimentary seeds sexual selection Silurian slight South America stamens sterility structure successive supposed swimbladder tend theory tion trees variability variations varieties vary whilst whole wings young