The Descent of Man

Lastly, one single member of the immense and
diversified class of fishes, namely, the lancelet
or amphioxus, is so different from all other fishes,
that Haeckel maintains that it ought to
form a distinct class in the vertebrate kingdom.
This fish is remarkable for its negative characters;
it can hardly be said to possess a brain,
vertebral column, or heart, etc.; so that it was
classed by the older naturalists amongst the
worms. Many years ago Prof. Goodsir perceived
that the lancelet presented some affinities
with the Ascidians, which are invertebrate,
hermaphrodite, marine creatures permanently
attached to a support. They hardly appear like
animals, and consist of a simple, tough, leathery
sack, with two small projecting orifices.
They belong to the Mulluscoida of Huxley—a
lower division of the great kingdom of the Mollusca;
but they have recently been placed by
some naturalists amongst the Vermes or
worms. Their larvae somewhat resemble tadpoles
in shape (23. At the Falkland Islands I had