The American Naturalist, المجلد 46Essex Institute, 1912 |
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عبارات ومصطلحات مألوفة
acters agouti alcohol aleurone Alive+young American Ancestors Starved animals appear Asplanchna bees biennis biological biotypes brachycephaly breeding campanulate cells cent char chromosomes classes Coefficient of variation color comparison correlation crayfish cross culture described determiners dolichocephaly dominant eggs endosperm Enothera entelechy evidence evolution experimental experiments F₂ fact factors fecundity female fertilization fishes flora flowers gametic genera genetic genotype genus germ grandiflora gymnosperms heredity heterozygotes heterozygous homozygotic homozygous honey horse humped hybrid individuals inheritance Jungermanniales Lamarckiana lampreys large number larvæ liverworts male Marchantiales mating means Mendelian Mendelism ment mutation nature observed occur offspring organisms origin paleobotany paleozoic parent pigment plants pods possible present Probable Error problem produced pure purple race ratio rosettes rotifers saccate seeds seems segregation selection shown species Standard deviation strains structure TABLE tion tissue unit characters yellow young zygote
مقاطع مشهورة
الصفحة 202 - All degrees of continuity between phenotypes may be found, but real genetic transitions must be distinguished from the transitions which we find in museums. Genotypes, it is true, can only be examined by the qualities and reactions of the phenotypes. Such examination shows that within pure lines — if no new mutations or other disturbances have been at work — there are no genotypical differences in the characters under examination. The only real discontinuity is that between different genotypes....
الصفحة 717 - ... a thin unsubstantial human image, in its nature a sort of vapor, film or shadow; the cause of life and thought in the individual it animates ; independently possessing the personal consciousness and volition of its corporeal owner, past or present; capable of leaving the body far behind to flash swiftly from place to place; mostly impalpable and invisible, yet also manifesting physical power, and especially appearing to men waking or asleep as a...
الصفحة 278 - I HAVE hitherto sometimes spoken as if the variations — so common and multiform in organic beings under domestication, and in a lesser degree in those in a state of nature — had been due to chance. This, of course, is a wholly incorrect expression, but it serves to acknowledge plainly our ignorance of the cause of each particular variation.
الصفحة 253 - The principle formerly alluded to under the term of ANALOGICAL VARIATION has probably in these cases often come into play; that is, the members of the same class, although only distantly allied, have inherited so much in common in their constitution, that they are apt to vary under similar exciting causes in a similar manner; and this would obviously aid in the acquirement through natural selection of parts or organs, strikingly like each other, independently of their direct inheritance from a common...
الصفحة 487 - The probable number of homozygotes and any particular class of heterozygotes in any generation r is found by expanding the binomial 1 + (2r - 1)" where n represents the number of character pairs involved. The exponent of the first term gives the number of heterozygous and the exponent of the second term the number of homozygous characters.
الصفحة 189 - So under nature with the nascent giraffe, the individuals which were the highest browsers and were able during dearths to reach even an inch or two above the others, will often have been preserved ; for they will have roamed over the whole country in search of food.
الصفحة 372 - The effects of this check on man are more complicated. Impelled to the increase of his species by an equally powerful instinct, reason interrupts his career, and asks him whether he may not 'bring beings into the world for whom he cannot provide the means of support.
الصفحة 372 - Among plants and animals the view of the subject is simple. They are all impelled by a powerful instinct to the increase of their species, and this instinct is interrupted by no reasoning or doubts about providing for their offspring. Wherever therefore there is liberty, the power of increase is exerted, and the superabundant effects are repressed afterwards by want of room and nourishment, which is common to animals and plants, and among animals, by becoming the prey of others.
الصفحة 128 - O unwearied feet, travelling ye know not whither ! Soon, soon, it seems to you, you must come forth on some conspicuous hilltop, and but a little way further, against the setting sun, descry the spires of El Dorado. Little do ye know your own blessedness ; for to travel hopefully is a better thing than to arrive, and the true success is to labour.
الصفحة 213 - The development of strongly marked climatic zones, at least between the polar circles, is, then, "exceptional and abnormal, and we have no evidence that in any other post-Silurian period, with the possible exception of the Permo-Carboniferous period, has the climatic distribution and segregation of life been so highly differentiated and complicated as in post-Tertiary times."1 The regular and normal conditions which have existed for vastly the greater part of geologic time, have been marked by relative...