Though Goethe did not work out a criterion of the homology of parts with any great clearness, he had an inkling of the principle later developed by E. Geoffroy St Hilaire, and called by him the "Principle of Connections." According to this principle, the homology of a part is determined by its position relative to other parts. Goethe expresses it thus:--"On the other hand the most constant factor is the position in which the bone is invariably found, and the function to which it is adapted in the organic edifice."[75] But from this sentence it is not clear that Goethe understood the principle as one of form independent of function, for he seems to consider that the homology of an organ is partly determined by the function which it performs for the whole. He wavers between the purely formal or morphological interpretation of the principle of connections and the functional. We find him in the additions to the _Entwurf_ (1796), saying:--"We must take into consideration not merely the spatial relations of the parts, but also their living reciprocal influence, their dependence upon and action on one another." [76] But in seeking for the intermaxillary bone in man he was guided by its position relative to the maxillaries--it must be the bone between the anterior ends of the maxillaries, a bone whose limits are indicated in the adult only by surface grooves. As a matter of fact Goethe's morphological views are neither very clearly expressed nor very consistent. This comes out in his treatment of the relation between structure and function. Sometimes he takes the view that structure determines function. "The parts of the animal," he writes, "their reciprocal forms, their relations, their particular properties determine the life and habits of the creature."[77] We are not to explain, he says, the tusks of the _Babirussa_ by their possible use, but we must ask how it comes to have tusks. In the same way we must not suppose that a bull has horns in order to gore, but we must investigate the process by which it comes to have horns to gore with. This is the rigorous morphological view. On the other hand he admits elsewhere that function may influence form. Apparently he did not work out his ideas on this point to logical clearness, and Radl[78] is probably correct in saying that the following quotation with its double assertion represents most nearly Goethe's position:-- "Also bestimmt die Gestalt die Lebensweise des Thieres, Und die Weise zu leben, sie wirkt auf alle Gestalten Maechtig zurueck."[79]