Contributions Volume 14

Contributions Volume 14

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1909 edition. Excerpt: ...large proportion of females that were obtained, that nitrogenous food favors the production of females, as Yung ('85) has maintained. The excess of females does not seem to me sufficiently large, however, to warrant such a conclusion. Moreover my previous experiments showed that in a total of 464 individuals that received an exclusive meat diet only 246, or 53.01 per cent., were females, thus making it highly improbable that nitrogenous food has any influence on the determination of sex in Bufo. III. Tm: INFLUENCE or TI-IE RIPENESS or TEE Eco AT THE TIME or FERTILIZATION ON SEX-DETERMINATION IN BUFO. For several years past Hertwig ('05--'07) has been investigating the problem of sex-determination, principally in various species of Rana, and he has already published three contributions to the literature on this subject. In his first paper, which appeared in I905, Hertwig ('05) suggests that the sexual character of an egg changes during the course of its development in the ovary. In the early stages of its ripening the egg tends to produce a male; in the middle phase of its ripening its tendency is towards the production ofa female; and in later phases, when the egg is overripe, it again _ shows a tendency to developinto a male. This change in the sexual character of the egg Hertwig ascribes in his second paper ('06) to " einem verschiedenen Wechselverhaltnis ihrer I-Iauptbestandteile, der Kernsubstanz und des Protoplasma.... Eier, welche relativ armer an Kernsubstanz sind, Weibchen liefern, chromatinreichere dagegen Mannchen." In his latest communication Hertwig ('07) lays little emphasis on the second part of his theory, but he seems to consider that the results of his experiments warrant the conclusion that...show more

Product details

  • Paperback | 140 pages
  • 189 x 246 x 8mm | 263g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236866843
  • 9781236866844