An introduction to the study of heredity / by E.W. Macbride.

  • MacBride, E. W. (Ernest William), 1866-1940.
Date:
[1924]
Catalogue details

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

Credit: An introduction to the study of heredity / by E.W. Macbride. Source: Wellcome Collection.

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    CHAPTER III THE DEVELOPMENT OF THE GERM INTO THE ADULT When the germ-cells have united with one another, and the zygote has been formed, it has, of course, a long period of development to undergo before it attains the adult form. From this development some important facts can be gleaned about the nature and mechan ism of heredity. This is especially true of animal development, and we may now indicate a few general points in the nature of this. The egg of one of the higher animals begins its development by dividing into a number of cells, which are termed blastomeres; this process is known as segmentation. Then these cells are moulded, by folding, into the primary organs or germinal layers. Of these there are three, viz. the ectoderm or primary skin, the endoderm or primary gut-wall, and the mesoderm or primary lining of the body-cavity. This process is known as the formation of the layers. Finally, these primary organs, by further processes of growth and 53