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abdomen appear birds breeding carried castrated cells chro classes of sperm color combinations condition conjugation cross Darwin diagram egg nucleus eggs eggs produce embryo evidence evolution evolution of sex fact factor for horns female Fig female-producing sperm fertilized eggs flies four gametes germ-cells give gray gray-red gynandromorph half heredity hermaphroditic hornless hybrid hydatina inbred individuals insects kind long-winged males and females mated Mendel's Mendelian micronuclei mosomes normal male number of chromosomes offspring ovary paramcecium parent parthenogenetic parthenogenetic female polar bodies pollen race red-eyed male reproduction Rhabditis secondary sexual characters self-fertilization sex chromo sex chromosomes sex factor sex glands sex ratio sex-determination sex-linked sex-linked characters sex-linked inheritance sexual egg sexual females sexual reproduction sexual selection shown species sperm spermatocyte spermatogenesis spermatozoa stage strains synapsis take place theory tilized tion vigor white eyes white-eyed male wings yellow
Page 101 - This depends, not on a struggle for existence, but on a struggle between the males for possession of the females ; the result is not death to the unsuccessful competitor, but few or no offspring. Sexual selection is, therefore, less rigorous than natural selection. Generally, the most vigorous males, those which are best fitted for their places in nature, will leave most progeny.
Page 114 - ... admire or even notice this display. The hen, the turkey, and the pea-fowl go on feeding while the male is displaying his finery ; and there is reason to believe that it is his persistency and energy rather than his beauty which wins the day.
Page 101 - The result is not death to the unsuccessful competitor, but few or no offspring. Sexual selection is, therefore, less rigorous than natural selection. Generally, the most vigorous males, those which are best fitted for their places in nature, will leave most progeny. But in many cases, victory depends not so much on general vigour, as on having special weapons, confined to the male sex.
Page 102 - I have seen the female sitting quietly on a branch, and two males displaying their charms in front of her. One would shoot up like a rocket, then suddenly expanding the snow-white tail like an inverted parachute, slowly descend in front of her, turning around gradually to show off both back and front.
Page 103 - The expanded white tail covered more space than all the rest of the bird, and was evidently the grand feature in the performance.
Page 217 - The failure to self-fertilize, which is the main problem, would seem to be due to the similarity in the hereditary factors carried by the eggs and sperm; but in the sperm, at least, reduction division has taken place prior to fertilization, and therefore unless each animal was homozygous (which from the nature of the case cannot be assumed possible) the failure to fertilize cannot be due to homozygosity. But both sperm and eggs have developed under the influence of the total or duplex number of hereditary...
Page 115 - In this chapter he described many of the dances, songs, and love-antics of birds, but regarded all such phenomena as merely "periodical fits of gladness." While, however, we may quite well agree with Mr. Hudson that conscious sexual gratification on the part of the female is not the cause of music and dancing performances in birds, nor of the brighter colors and ornaments that distinguish the male, such an opinion by no means excludes the conclusion that these phenomena are primarily sexual and intimately...
Page 114 - To conscious sexual selection, that is, the actual choice by the females of the more brilliantly-coloured males, I believe very little if any effect is directly due. It is undoubtedly proved that in birds the females do sometimes exert a choice ; but the evidence of this fact collected by Mr. Darwin (Descent of Man, chap, xiv.) does not prove that colour determines that choice, while much of the strongest evidence is directly opposed to this view.