III. Experiments on the development of chick and duck embryos, cultivated in vitro

The experimental study of the developmental mechanics of the birds, and of the higher vertebrates in general, has hitherto been particularly difficult, since it has been impossible to keep the embryos alive in a situation in which the necessary manipulations can be successfully carried out. In the circumstances our knowledge of the subject is practically confined to such aspects as can be investigated by the method of isolation ; that is to say, chiefly to the aspect of self-differentiation.