The determination of sex / by L. Doncaster.

  • Doncaster, L. (Leonard), 1877-1920.
Date:
1914
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: The determination of sex / by L. Doncaster. Source: Wellcome Collection.

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    I] The Problem 5 that egg into a female, therefore all females are derived from eggs which contain A. They very probably may be, but that they are must be shown by independent proof. With this introduction we may proceed to state the problem before us. Put shortly, it is to find explanations for the following facts. In the great majority of animals, and in many plants, every individual is either male or female. In each species there is a fairly constant average ratio between the number of males and females born ; this ratio is commonly not far from equality, but varies con¬ siderably from species to species. In most animals and in some plants the difference between male and female does not concern only the organs directly connected with reproduction, but affects various parts of the body to a greater or less degree, so that the sexes are more or less readily recognisable by so-called secondary sexual characters, such as the antlers of deer or the beard of man. Not rarely the differences are very striking, as in the peacock among birds, and finally we get the most extreme cases of sexual dimorphism, as in the marine worm Bonellia (Plate I, fig. i), in which the male is an almost microscopic parasite Hving in the body of the female, or in moths of the family Psychidae, and in some foreign species of Orgyia, in which the female is so degenerate as to be unable to leave the cocoon. These facts—the existence of two distinct sexes, the comparative regularity of the ratio in which they are produced, and the development of secondary sexual characters—are