Sex / by Patrick Geddes ... and J. Arthur Thomson.

  • Patrick Geddes
Date:
[1914]
Catalogue details

Licence: In copyright

Credit: Sex / by Patrick Geddes ... and J. Arthur Thomson. Source: Wellcome Collection.

    49/280 page 45
    with its asexual, hermaphrodite, unisexual, and parthenogenetic forms, is a very epitome of the evolution of sex. Testes and Ovaries.—In a sponge, which shows no organs in the strict sense, and only the beginnings of tissues, the germ-cells appear sporadically in the middle stratum (or meso- gloea) of the body, and both sperms and ova may be seen developing in the same sponge. An important step was taken, however, when the formation of gametes began to be localised and when these foci of gamete-making began to be enclosed, protected, and nourished by adjacent tissue. At first, doubtless, the differ- ence between the egg-multiplying gonads (or ovaries) and the sperm-multiplying gonads (or testes) was only to be detected with the microscope, though it was very profound. But gradually there came about a specialisa- tion of the accessory parts in relation to the deeply different functions of egg-multiplying and sperm-multiplying, and recognisably dif- ferent ovaries and testes were established. Furthermore, there came to be associated with ovaries and testes a good deal of auxiliary tissue that had nothing directly to do with oogenesis or spermatogenesis. Accessory glands and ducts were formed. It is probable that variations or mutations involving the tissue in the vicinity of the reproductive organs have been from time to time caught up into their service, and it is not necessary to suppose that these advan- tageous accessions, such as having a yolk- gland near the ovary, arose as pure coinci- dences. For it is a well-known fact (whether
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