the spinal cord; but the lower part apparently consists merely of the
pia mater, or vascular investing membrane. Even in this case the os
coccyx may be said to possess a vestige of so important a structure as
the spinal cord, though no longer enclosed within a bony canal. The
following fact, for which I am also indebted to Prof. Turner, shews how
closely the os coccyx corresponds with the true tail in the lower
animals: Luschka has recently discovered at the extremity of the
coccygeal bones a very peculiar convoluted body, which is continuous
with the middle sacral artery; and this discovery led Krause and Meyer
to examine the tail of a monkey (Macacus), and of a cat, in both of
which they found a similarly convoluted body, though not at the
extremity.
The reproductive system offers various rudimentary structures; but
these differ in one important respect from the foregoing cases. Here we
are not concerned with the vestige of a part which does not belong to
the species in an efficient state, but with a part efficient in the one
sex, and represented in the other by a mere rudiment. Nevertheless, the
occurrence of such rudiments is as difficult to explain, on the belief
of the separate creation of each species, as in the foregoing cases.
Hereafter I shall have to recur to these rudiments, and shall shew that
their presence generally depends merely on inheritance, that is, on
parts acquired by one sex having been partially transmitted to the
other. I will in this place only give some instances of such rudiments.
It is well known that in the males of all mammals, including man,
rudimentary mammae exist. These in several instances have become well
developed, and have yielded a copious supply of milk. Their essential
identity in the two sexes is likewise shewn by their occasional
sympathetic enlargement in both during an attack of the measles. The
vesicula prostatica, which has been observed in many male mammals, is
now universally acknowledged to be the homologue of the female uterus,
together with the connected passage. It is impossible to read
Leuckart s able description of this organ, and his reasoning, without
admitting the justness of his conclusion. This is especially clear in
the case of those mammals in which the true female uterus bifurcates,
for in the males of these the vesicula likewise bifurcates. (54.
Leuckart, in Todd s Cyclopaedia of Anatomy 1849-52, vol. iv. p. 1415.
In man this organ is only from three to six lines in length, but, like
so many other rudimentary parts, it is variable in development as well
as in other characters.) Some other rudimentary structures belonging to
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