Exactly in those respects in which the developing Man differs from the
Dog, he resembles the ape, which, like man, has a spheroidal yolk-sac
and a discoidal, sometimes partially lobed, placenta. So that it is
only quite in the later stages of development that the young human being
presents marked differences from the young ape, while the latter departs
as much from the dog in its development, as the man does.
Startling as the last assertion may appear to be, it is demonstrably
true, and it alone appears to me sufficient to place beyond all doubt
the structural unity of man with the rest of the animal world, and more
particularly and closely with the apes.
Thus, identical in the physical processes by which he
originates--identical in the early stages of his formation--identical in
the mode of his nutrition before and after birth, with the animals which
lie immediately below him in the scale--Man, if his adult and perfect
structure be compared with theirs, exhibits, as might be expected, a
marvellous likeness of organisation. He resembles them as they resemble
one another--he differs from them as they differ from one another.