1. The heart was removed from chick embryos of seven to twelve somites, and the embryos cultivated in vitro. The operation abolished the normal twisting of the anterior part of the embryo on to its left side and the general bending of the brain region into an arc. These two processes therefore seem to be dependent on the normal development of the heart.

2. The embryos showed a bending of the forebrain relative to the midbrain, which is therefore independent of the development of the heart.

3. The embryonic blood system, including the aortic arches, developed normally in many cases, but the blood vessels became enormously dilated.

4. The lateral evaginations of the foregut and the visceral arch mesenchyme underwent the first stages of differentiation in atypical positions, seemingly independently of each other or of any other structures.

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