C. H. Waddington

Towards a Theoretical Biology

Two symposia on theoretical biology were held in 1966 and 1967 at the instigation of the International Union of Biological Sciences. The meetings were organized by Professor Waddington, and in this article he outlines some of the points discussed at the meetings. The essays arising from the first symposium have recently been published under the title Towards a Theoretical Biology.

Induction by the endoderm in birds

Summary1.The endoderm was separated from the epiblast in chick and duck embryos of young primitive streak stages, and then the two layers of tissue were replaced so that their longitudinal axes were diametrically opposed: i. e. the anterior part of the endoderm lay under the posterior region of the epiblast, and the posterior part of the endoderm under the anterior region of the epiblast. The combination was then cultivatedin vitro by the watch-glass technique.2.The displaced endoderm had in most cases an effect on the development of the epiblast. It either (1) hindered the normal growth in length of the primitive streak, or (2) caused the development of a new primitive streak. In some cases the secondary (induced) streak disappeared on further cultivation, in some cases both streaks persisted and gave rise to a double monster, and in still other cases the secondary streak persisted and the primary disappeared. In two cases primary and secondary united to form a single semicircular embryo.3.It is argued that the endoderm does not induce the differentiation of a definite tissue, but that it induces the form-building movements which lead to the development of the primitive streak.Zusammenfassung1.Bei Hühner- und Entenembryonen im frühen Primitivstreifenstadium wurden Entoderm und Epiblast voneinander gelöst und darauf wieder in umgekehrter Richtung vereinigt: d. h. der vordere Teil des Entoderms kam unter das Hinterende des Epiblasts, und der hintere Teil des Entoderms unter das Vorderende des Epiblasts zu hegen. Diese Kombination wurde dannin vitro mit der Uhrschälchenmethode gezüchtet.2.In den meisten Fällen übt das verlagerte Entoderm einen Einfluß auf das darüberliegende Epiblast aus. Es konnte entweder 1. das normale Wachstum des Primitivstreifens verhindern, oder 2. die Bildung eines neuen Primitivstreifens veranlassen. Dieser neue induzierte Primitivstreifen lag dann zu dem primären in entgegengesetzter Richtung. In einigen Fällen verschwand dieser sekundäre Streifen bei weiterer Züchtung, in anderen kamen beide Streifen zur Weiterentwicklung und führten so zu einer Doppelbildung, in wieder anderen Fällen verschwand der primäre Streifen, während der sekundäre sich weiterentwickelte. Bei zwei Experimenten vereinigten sich Primäre und Sekundäre zu einem halbkreisförmigen Embryo.3.Es wird daraus gefolgert, daß das Entoderm nicht die Differenzierung wohl definierten Gewebes induziert, sondern die Formbildungs-bewegungen, die zur Primitivstreifenbildung führen.

Air Raid Precautions

WHILE we appreciate the fulness of the treatment which has been accorded to our book “The Protection of the Public from Aerial Attack”, we should be grateful for the opportunity of commenting on certain points in the review in NATURE of April 10, p. 606. Regarding the purpose of the book, General Foulkes says, “It suggests no better defensive measures than those recommended by the Home Office”. Better methods are not lacking, and our object simply was to provide some scientific data concerning the proposed precautions—because no such data had been published and we felt that the unsupported statements of Government spokesmen concerning their efficiency were no substitute for scientific fact.