d is normally concealed beneath the
flesh, but in the embryo the tail projects freely and is movable. Up to
the sixth month of the ante-natal sleep the body is covered, all but the
palms and soles, with longish hair (the lanugo), which usually
disappears before birth. This is a stage in the normal development,
which is reasonably interpreted as a recapitulation of a stage in the
racial evolution. We draw this inference when we find that the unborn
offspring of an almost hairless whale has an abundant representation of
hairs; we must draw a similar inference in the case of man.

It must be noticed that there are two serious errors in the careless
statement often made that man in his development is at one time like a
little fish, at a later stage like a little reptile, at a later stage
like a little primitive mammal, and eventually like a little monkey. The
first error here is that the comparison should be made with
_embryo_-fish, _embryo_-reptile, _embryo_-mammal, and so on. It is in
the making of the embryos that the great resemblance lies. When the
human embryo shows the laying down of the essential vertebrate
characters, such as brain and spinal cord, then it is closely comparable
to the embryo of a lower vertebrate at a similar stage. When, at a
subsequent stage, its heart, for instance, is about to become a
four-chambered mammalian heart, it is closely comparable to the heart
of, let us say, a turtle, which never becomes more than three-chambered.
The point is that in the making of the organs of the body, say brain and
kidneys, the embryo of man pursues a path closely corresponding to the
path followed by the embryos of other backboned animals lower in the
scale, but at successive stages it parts company with these, with the
lowest first and so on in succession. A human embryo is never like a
little reptile, but the developing organs pass through stages which very
closely resemble the corresponding stages in lower types which are in a
general way ancestral.

The second error is that every kind of animal, man included, has from
the first a certain individuality, with peculiar characteristics which
are all its own. This is expressed by the somewhat difficult word
_specificity_, which just means that every species is itself and no
other. So in the development of the human embryo, while there are close
resemblances to the embryos of apes, monkeys, other mammals, and even,
at earlier stages still, to the embryos of rept