organs often are only
developed, proportionally with other parts, in the embryonic or young
state of each species{495}; this again, especially considering the
classificatory importance of abortive organs, is evidently part of the
law (stated in the last chapter) that the higher affinities of organisms
are often best seen in the stages towards maturity, through which the
embryo passes. On the ordinary view of individual creations, I think
that scarcely any class of facts in natural history are more wonderful
or less capable of receiving explanation.

{492} The case of rudimentary organs adapted to new purposes is
discussed in the _Origin_, Ed. i. p. 451, vi. p. 620.

{493} This is here stated on the authority of Sprengel; see also
_Origin_, Ed. i. p. 452, vi. p. 621.

{494} _Origin_, Ed. i. p. 455, vi. p. 627. In the margin R. Brown's
name is given apparently as the authority for the fact.

{495} _Origin_, Ed. i. p. 455, vi. p. 626.

_The abortive organs of physiologists._

Physiologists and medical men apply the term "abortive" in a somewhat
different sense from naturalists; and their application is probably the
primary one; namely, to parts, which from accident or disease before
birth are not developed or do not grow{496}: thus, when a young animal
is born with a little stump in the place of a finger or of the whole
extremity, or with a little button instead of a head, or with a mere
bead of bony matter instead of a tooth, or with a stump instead of a
tail, these parts are said to be aborted. Naturalists on the other hand,
as we have seen, apply this term to parts not stunted during the growth
of the embryo, but which are as regularly produced in successive
generations as any other most essential parts of the structure of the
individual: naturalists, therefore, use this term in a metaphorical
sense. These two classes of facts, however, blend into each other{497};
by parts accidentally aborted, during the embryonic life of one
individual, becoming hereditary in the succeeding generations: thus a
cat or dog, born with a stump instead of a tail, tends to transmit
stumps to their offspring; and so it is with stumps representing the
extremities; and so again with flowers, with defective and rudimentary
parts, which are annually produced in new flower-buds and even in
successive seedlings. The strong hereditary tendency to reproduce every
either congenital or slowly acquired structu