File:Heredity and sex (1913) (14594308657).jpg

Identifier: hereditysex1913morg (find matches)
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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ustrating chromosome aycLe_in Neuroterus. -4.. one tj^pe ofspring female, -^-hose eggs (containing 20 chromosomes) produce no polarbodies. Only sexual females result. B, the other t^^pe of spring femalewhose eggs form two polar bodies, leaA-ing 10 chromosomes in egg. Theseeggs give rise to males. C, ripening of egg of sexual female (2d generation),and Z), spermatogenesis of male (second generation). These eggs produce sexual females (in left-hand sideof Fig. 91). From the eggs of other parthenogenetic fe-males two polar bodies are given off, and the haff (10)number of chromosomes is left in the egg (see right-handside of Fig. 91). These eggs produce males. The life 178 HEREDITY AND SEX cycle finds its explanation in these relations except thatthe origin of the two kinds of parthenogenetic femalesis unexplained. If we were justified in assuming thattwo classes of female-producing sperm are made in themale, even this point would be cleared up, for in this ^^//^//f.rfrr/ rY/y//a/r/7/i^/U
Text Appearing After Image:
fl Iff (ri nf. \/.>7(-rf</e( t % ^C/ Fig. 92. — Life cycle of Phylloxera caryoecaulis. way the two classes of parthenogenetic females couldbe explained. In another group of insects, the aphids and phyllox-erans, the situation is different. In the phylloxerans of the hickories there emergesin the spring, from a fertilized egg, a female known asthe stem mother (Fig. 92). She pierces a young leaf PARTHENOGENESIS 179 with her proboscis, which causes a prohferation of thecells of the leaf. Eventually the leaf cells grow so fastthat the stem mother is overarched in the gall that shehas called forth. Inside the gall she begins to lay her eggs. From theseeggs emerge young individuals that remain in the galluntil they pass their last molt, when they become wingedmigrants. Externally all the migrants are alike; butif they are dissected, it will be found that some of themhave large eggs, some small eggs. But all the offspringof the same mother are of one or of the other sort. The migrant

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