Einige tolle Sex Bilder:

Image from page 138 of “Heredity and sex” (1913)
Sex
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Identifier: hereditysex1913morg
Title: Heredity and sex
Year: 1913 (1910s)
Authors: Morgan, Thomas Hunt, 1866-1945
Subjects: Heredity Sex Heredity
Publisher: New York, Columbia University Press
Contributing Library: Francis A. Countway Library of Medicine
Digitizing Sponsor: Open Knowledge Commons and Harvard Medical School

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Johannsen.) the tops of the beans, the line gives a curve like thatshown in Fig. 62. This is known as the curve of prob-ability. The curve can be, of course, most readilymade by making the measurements directly. Mostindividuals of such a population will have the charac-ter developed to the degree represented by the highestpoint in the curve. Now if two individuals standingat one side (let us say with the character in questionbetter developed than the average) become the parent 124 HEREDITY AND SEX of the next generation, their offspring will make a newcurve that has moved, so to speak, in the direction ofselection (Fig. 63). If again two more extreme individuals are selected,another step is taken. The process is assumed to goon as long as the selection process is maintained. So the matter stood until a Danish botanist, Johann-sen, set seriously to work to test the validity of theassumption, using a race of garden beans for his meas-urements. He discovered in the first place that popu-

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FiG. 63. — Schematic representation of the type-shifting effect of selec-tion from the point of view of Galtons reversion theory. The * marks thepoint on the curves oi A, Ai, A2 from which the selection is supposed to bemade. (Goldschmidt.) lations are made up of a number of races or ^purelines. When we select in such a population we sortout and separate its constituent races, and sooneror later under favorable conditions can get a purerace. Selection has created nothing new; it haspicked out a particular preexisting race from a mixedpopulation. Johannsen has shown that within a pure line selec-tion produces no effect, since the offspring form thesame group with the same mode as the group from whichthe parents came. The variability within the purelines is generally ascribed to environmental influences SECONDARY SEXUAL CHARACTERS 125 which are recurrent in each generation. The germ-plasm is homogeneous for all members of the pure line,while in a mixed population the germ-plasm is not

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Image from page 35 of “Heredity and sex” (1913)
Sex
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Identifier: hereditysex00morg
Title: Heredity and sex
Year: 1913 (1910s)
Authors: Morgan, Thomas Hunt, 1866-1945
Subjects: Heredity Sex
Publisher: New York, N.Y. : Columbia University Press
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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1^. ^ ■•^:- ^^^ ^^ Hf O Fig. 8. — Origin of germ-cells in Miastor. Note small black proto-plasmic area at bottom of egg into which one of the migrating segmentationnuclei moves to produce the germ-cells. (After Kahle.) 22 HEREDITY AND SEX single cell that retains all of the chromatin in its nucleusgives rise to the germ-cells. In a marine worm-like form, sagitta, two cells caneasily be distinguished from the other cells in the wall ofthe digestive tract (Fig. 7). They leave their first posi-tion and move into the interior of the body, where theyproduce the ovary and testes. Lcpldosteus Lepldosteus ChrLjsemys

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Image from page 147 of “Heredity and sex” (1913)
Sex
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Identifier: hereditysex1913morg
Title: Heredity and sex
Year: 1913 (1910s)
Authors: Morgan, Thomas Hunt, 1866-1945
Subjects: Heredity Sex Heredity
Publisher: New York, Columbia University Press
Contributing Library: Francis A. Countway Library of Medicine
Digitizing Sponsor: Open Knowledge Commons and Harvard Medical School

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About This Book: Catalog Entry
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in nature associated with onesex alone. It has long been recognized in mammals and birdsthat there is a close connection between sexual maturityand the full development of the secondary sexual char-acters. This relation suggests some intimate correla-tion between the two. It has been shown, in fact, insome mammals at least, that the development of thesecondary sexual characters does not take place, orthat they develop imperfectly, if the sex glands areremoved. It may appear, therefore, that we are deal-ing here with a purely physiological process, and that 132 THE EFFECTS OF CASTRATION 133 the development of these structures and colors is a by-product of sex itself, and calls for no further explana-tion. But the question cannot be so hastily dismissed.This can best be shown by taking up at once the ma-terial at hand. OPERATIONS ON MAMMALS In the deer, the facts are very simple. If the veryyoung male is castrated before the knobs of the antlershave appeared, the antlers never develop.

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Fig. 67. — Merino; male (horned) and female (hornless). If the operation is performed at the time when theantlers have already begun to develop, incompletedevelopment takes place. The antlers remain coveredby the velvet and are never thrown off. They are calledperuke antlers. If the adult stag is castrated whenthe horns are fully developed, they are precociously 134 HEREDITY AND SEX dropped, and are replaced, if at all, by imperfect ant-lers, and these are never renewed. These facts make it clear that there is an intimaterelation between the orderly sequence of developmentof the horns in the deer and the presence of the malesexual glands. In the case of sheep, the evidence is more explicit.Here we have carefully planned experiments in whichboth sexes have been studied; and there are breeding

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