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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    subsequent heterogeneity to its infiltration by materials given off from the nucleus, and we have already learnt that the material of the nucleolus is ejected into the protoplasm; these materials obviously give rise to the different organ-forming substances. This hypothesis is completely borne out when we examine the egg of the sea-squirt Cynthia. Here also we find strongly localized organ-forming substances. Indeed, in one species they are distinguishable in the living egg by their different colours. If we examine the ripening egg we find that streams of minute granules of chromatin are pouring into the protoplasm from the nucleus. Further, in the development of the species (Cynthia partita) in which the different organ-forming substances are distinguished by different colours it has been shown by an American zoologist (Conklin) that the ectoderm of the embryo is formed from the fluid contents or sap of the nucleus of the egg. When the egg ripens and the nuclear membrane is dissolved the escaping sap forms a cap of clear material at one side of the egg, and when its develop ment is followed it is found to be changed into the ectoderm or primitive skin of the young animal.