remaining. Now the turbellarian is small and sluggish, with a fair
digestive system. With a great amount of nutriment at its disposal
the reproductive system came rapidly to a high development, and
relatively to other organs stands higher than it almost ever will
again.

[Footnote A: Cf. p. 35.]

It is only fair to state that good authorities hold that so
primitive an animal could not originally have had so highly
developed a system, and that this characteristic must be acquired,
not ancestral.

That certain portions of it may be later developments may be not
only possible but probable. But anyone who has carefully studied the
different groups of worms, will, I think, readily grant that in the
stage of these flat worms reproduction was the dominant function,
which had most nearly attained its possible height of development.
From this time on the muscular and nervous systems were to claim an
ever-increasing share of the nutriment, and the balance for
reproduction is to grow smaller.

At the close of this lecture I wish to describe very briefly a
hypothetical form. It no longer exists; perhaps it never did. But
many facts of embryology and comparative anatomy point to such a
form as a very possible ancestor of all forms higher than flat
worms, viz., mollusks, arthropods, and vertebrates.

It was probably rather long and cylindrical, resembling a small
and short earthworm in shape. The skin may have been much like