[Illustration: FIG. 6. Two right hind feet of polydactyle cats. _II_ shows the lowest development of the condition yet recorded. The digit, _d_^{1}, which stands as hallux is fully formed and has three phalanges. Both it and the digit marked _d_^{2} are formed as _left_ digits. In the normal hind foot of the cat the hallux is represented by a rudiment only. _I_ shows a further development of the condition. In this foot there are _six_ digits. _d_^{1} has two phalanges, but both it and _d_^{2} and _d_^{3} are shaped as left digits. Thus _d_^{3}, which in the normal foot would be shaped as a right digit, is transformed so as to look like a _left_ digit.] The phenomenon in this case can hardly be regarded as due to the excitation of dormant buds, for it is apparent on examination that the new growths are not placed in any fixed geometrical relation to the original plant. They arise on the petiole, for example, as small green outgrowths each of which gradually becomes a tiny leaf. The attitude of these leaves is quite indeterminate, and they may point in any direction, some having their apices turned peripherally, some centrally, and others in various oblique or transverse positions (Fig. 5). These little leaves are thus comparable with seedlings, in that their polarity is not related to, or consequent upon that of the parent plant. They have in fact that "individuality," which we associate with germinal reproduction. There are many curious phenomena seen in the behaviour of parts normally repeated in bilateral symmetry which may some day guide us towards an understanding of the mechanics of division. A part like a hand, which needs the other hand to complete its symmetry, cannot twin by mere division, yet by proliferation and special modifications on the radial side of the same limb, even a hand may be twinned. In the well known polydactyle cats a change of this kind is very common and indeed almost the rule. When extra digits appear at the inner (tibial) side of the limb, they are shaped as digits of the other side, and even the normal digit II (index) is usually converted into the mirror-image of its normal self. The limb then develops a new symmetry in itself. Nevertheless it is not easy to interpret these facts as meaning that there has been some interruption in the control which one side of the body exercises over the other. The heredity of polydactylism is complex but there is little doubt that the condition familiar in the Cat is a dominant. In some human cases also the descent is that of a dominant, but irregularities are so frequent that no general rule can yet be perceived. The dominance of such a condition is an exception to the principle that the less-divided is usually dominant to the more-divided, a fact which probably should be interpreted as meaning that divisions are of more than one kind.