Rudimentary organs sometimes retain
their potentiality: this occasionally occurs with the mammae of male
mammals, which have been known to become well developed and to secrete
milk. So again in the udders of the genus Bos, there are normally four
developed and two rudimentary teats; but the latter in our domestic cows
sometimes become well developed and yield milk. In regard to plants, the
petals are sometimes rudimentary, and sometimes well developed in the
individuals of the same species. In certain plants having separated sexes
Kolreuter found that by crossing a species, in which the male flowers
included a rudiment of a pistil, with an hermaphrodite species, having of
course a well-developed pistil, the rudiment in the hybrid offspring was
much increased in size; and this clearly shows that the rudimentary and
perfect pistils are essentially alike in nature. An animal may possess
various parts in a perfect state, and yet they may in one sense be
rudimentary, for they are useless: thus the tadpole of the common
salamander or water-newt, as Mr. G.H. Lewes remarks, "has gills, and passes
its existence in the water; but the Salamandra atra, which lives high up
among the mountains, brings forth its young full-formed. This animal never
lives in the water. Yet if we open a gravid female, we find tadpoles
inside her with exquisitely feathered gills; and when placed in water they
swim about like the tadpoles of the water-newt.
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