On the Origin of Species by Means of Natural Selection: Or, The Preservation of Favoured Races in the Struggle for LifeCassell, 1909 - 430페이지 |
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44개의 결과 중 1 - 5개
20 페이지
... separated by any clear line of distinction from mere variations . But I am strongly inclined to suspect that the most frequent cause of variability may be attributed to the male and female reproductive elements having been affected ...
... separated by any clear line of distinction from mere variations . But I am strongly inclined to suspect that the most frequent cause of variability may be attributed to the male and female reproductive elements having been affected ...
39 페이지
... separating some very distinct variety , and breeding from it , the principle would be so obvious as hardly to be worth notice ; but its importance consists in the great effect produced by the accumulation in one direction , during ...
... separating some very distinct variety , and breeding from it , the principle would be so obvious as hardly to be worth notice ; but its importance consists in the great effect produced by the accumulation in one direction , during ...
53 페이지
... separated areas . How many of those birds and insects in North America and Europe , which differ very slightly from each other , have been ranked by one eminent naturalist as undoubted species , and by another as varieties , or , as ...
... separated areas . How many of those birds and insects in North America and Europe , which differ very slightly from each other , have been ranked by one eminent naturalist as undoubted species , and by another as varieties , or , as ...
89 페이지
... separation of the sexes of plants , presently to be alluded to . Some holly - trees bear only male flowers , which have four stamens producing a rather small quantity of pollen , and a rudimentary pistil ; other holly - trees bear only ...
... separation of the sexes of plants , presently to be alluded to . Some holly - trees bear only male flowers , which have four stamens producing a rather small quantity of pollen , and a rudimentary pistil ; other holly - trees bear only ...
90 페이지
... separation of the sexes of our plant would be advantageous on the principle of the division of labour , individuals with this tendency more and more increased , would be continually favoured or selected , until at last a complete separation ...
... separation of the sexes of our plant would be advantageous on the principle of the division of labour , individuals with this tendency more and more increased , would be continually favoured or selected , until at last a complete separation ...
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accumulated adapted affinities allied species America analogous ancient animals appear archipelago become bees believe birds breeds cause cells characters cirripedes climate closely allied colour continuous crossed crustaceans degree difficulty distinct species divergence domestic doubt embryo endemic existing exterminated extinct extremely facts favourable fertilised fertility flowers formations forms fossil Gärtner genera genus geological geological period Glacial period gradations greater number groups of species habits Hence hybrids hybrids produced important increase individuals inhabitants inherited insects instance instincts intercrossing intermediate larvæ laws less living males mammals manner migration modification modified descendants natural selection naturalists nearly nest occasionally offspring organic organisation origin of species perfect pigeons plants pollen present principle probably produced progenitor ranked reciprocal crosses remarked resemble rock-pigeon rudimentary seeds sexual sexual selection Silurian slight sometimes South America sterility structure struggle successive supposed swimbladder tend theory variability variations varieties vary whole widely