Fragments of heart from the same species, when cultivated in vitro, are capable of uniting and pulsating synchronously. This happens not only in fragments derived from the same heart but with those from different individuals of the same species. It was not possible, on the other hand, to obtain, under the conditions of experiment, any physiological union of a heart fragment from a duck embryo with one from a chicken embryo, though both pulsated in the same medium and though the tissue cells of the duck were capable of growth and multiplication.
From the experiments it is evident that cell contact is essential for the development of physiological identity as just described. Since such a physiological identity cannot be obtained through the union of a fragment of a duck heart and a fragment of a chicken heart, one may suppose that anastomosis between the cells must play a very significant rôle in it.