now supposed
to be represented in existing embryos, has not been obliterated, either by
the successive variations in a long course of modification having
supervened at a very early age, or by the variations having been inherited
at an earlier period than that at which they first appeared. It should also
be borne in mind, that the supposed law of resemblance of ancient forms of
life to the embryonic stages of recent forms, may be true, but yet, owing
to the geological record not extending far enough back in time, may remain
for a long period, or for ever, incapable of demonstration.

Thus, as it seems to me, the leading facts in embryology, which are second
in importance to none in natural history, are explained on the principle of
slight {450} modifications not appearing, in the many descendants from some
one ancient progenitor, at a very early period in the life of each, though
perhaps caused at the earliest, and being inherited at a corresponding not
early period. Embryology rises greatly in interest, when we thus look at
the embryo as a picture, more or less obscured, of the common parent-form
of each great class of animals.

_Rudimentary, atrophied, or aborted Organs._--Organs or parts in this
strange condition, bearing the stamp of inutility, are extremely common
throughout nature. For instance, rudimentary mammae are very general in the
males of mammals: I presume that the "bastard-wing" in birds may be safely
considered as a digit in a rudimentary state: in very many snakes one lobe
of the lungs is rudimentary; in other snakes there are rudiments of the
pelvis and hind limbs. Some of the cases of rudimentary organs are
extremely curious; for instance, the presence of teeth in foetal whales,
which when grown up have not a tooth in their heads; and the presence of
teeth, which never cut through the gums, in the upper jaws of our unborn
calves. It has even been stated on good authority that rudiments of teeth
can be detected in the beaks of certain embryonic birds. Nothing can be
plainer than that wings are formed for flight, yet in how many insects do
we see wings so reduced in size as to be utterly incapable of flight, and
not rarely lying under wing-cases, firmly soldered together!

The meaning of rudimentary organs is often quite unmistakeable: for
instance there are beetles of the same genus (and even of the same species)
resembling each other most closely in all respects, one of which will have
full-size