n of an antenna was developed. A case has been recorded[920] of a man
who had during both dentitions a double tooth in place of the left second
incisor, and he inherited this peculiarity from his paternal grandfather.
Several cases are known[921] of additional teeth having been developed in
the palate, more especially with horses, and in the orbit of the eye.
Certain breeds of sheep bear a whole crowd of horns on their foreheads.
Hairs occasionally appear in strange situations, as within the ears of the
Siamese hairy family; and hairs "quite natural in structure" have been
observed "within the substance of the brain."[922] As many as five spurs
have been seen on both legs in certain Game-fowls. In the Polish fowl the
male is ornamented with a topknot of hackles {392} like those on his neck,
whilst the female has one of common feathers. In feather-footed pigeons and
fowls, feathers like those on the wing arise from the outer side of the
legs and toes. Even the elemental parts of the same feather may be
transposed; for in the Sebastopol goose, barbules are developed on the
divided filaments of the shaft.

Analogous cases are of such frequent occurrence with plants that they do
not strike us with sufficient surprise. Supernumerary petals, stamens, and
pistils, are often produced. I have seen a leaflet low down in the compound
leaf of _Vicia sativa_ converted into a tendril, and a tendril possesses
many peculiar properties, such as spontaneous movement and irritability.
The calyx sometimes assumes, either wholly or by stripes, the colour and
texture of the corolla. Stamens are so frequently converted, more or less
completely, into petals, that such cases are passed over as not deserving
notice; but as petals have special functions to perform, namely, to protect
the included organs, to attract insects, and in not a few cases to guide
their entrance by well-adapted contrivances, we can hardly account for the
conversion of stamens into petals merely by unnatural or superfluous
nourishment. Again, the edge of a petal may occasionally be found including
one of the highest products of the plant, namely the pollen; for instance,
I have seen in an Ophrys a pollen-mass with its curious structure of little
packets, united together and to the caudicle by elastic threads, formed
between the edges of an upper petal. The segments of the calyx of the
common pea have been observed partially converted into carpels, including
ovules, and with