(Amphioxus), are descended from lower
invertebrates resembling the larvae of an existing Tunicate
(Appendicularia). From these primitive fishes were evolved higher fishes
of the ganoid type and others of the type of Lepidosiren (Dipneusta). It
is a very small step from these to the Amphibia:

"In the class of mammals the steps are not difficult to conceive which
led from the ancient Monotremata to the ancient Marsupials; and from
these to the early progenitors of the placental mammals. We may thus
ascend to the Lemuridae; and the interval is not very wide from these to
the Simiadae. The Simiadae then branched off into two great stems,
the New World and Old World monkeys; and from the latter, at a remote
period, Man, the wonder and glory of the Universe, proceeded." ("Descent
of Man" (Popular Edition), page 255.)

In these few lines Darwin clearly indicated the way in which we were
to conceive our ancestral series within the vertebrates. It is fully
confirmed by all the arguments of comparative anatomy and embryology,
of palaeontology and physiology; and all the research of the subsequent
forty years has gone to establish it. The deep interest in geology which
Darwin maintained throughout his life and his complete knowledge of
palaeontology enabled him to grasp the fundamental importance of the
palaeontological record more clearly than anthropologists and zoologists
usually do.

There has been much debate in subsequent decades whether Darwin himself
maintained that man was descended from the ape, and many writers
have sought to deny it. But the lines I have quoted verbatim from the
conclusion of the sixth chapter of the "Descent of Man" (1871) leave no
doubt that he was as firmly convinced of it as was his great
precursor Jean Lamarck in 1809. Moreover, Darwin adds, with particular
explicitness, in the "general summary and conclusion" (chapter XXI.) of
that standard work ("Descent of Man", page 930.):

"By considering the embryological structure of man--the homologies
which he presents with the lower animals,--the rudiments which he
retains,--and the reversions to which he is liable, we can partly recall
in imagination the former condition of our early progenitors; and can
approximately place them in their proper place in the zoological series.
We thus learn that man is descended from a hairy, tailed quadruped,
probably arboreal in its habits, and an inhabitant of the Old World.
This creature, if its whole structure