at should not be lost sight of.

Strange though it be, there are many creatures, among what we sometimes
call the 'lower order of creation,' which give promise of great things
during the earlier period of their lives, but later degenerate out of
all recognition.

Let us take one or two of the more remarkable instances. Many of you,
when at the seaside, must have found, clinging to rocks and shells,
peculiar, tough, leathery and somewhat bottle-shaped bodies, popularly
known as 'sea-squirts,' from their habit of squirting out water when
touched. But how many of you have any idea that these same 'squirts'
really belong to the great division of vertebrates or backboned animals?
Yet such is the case, though not even scientific men were aware of this
until the facts which I am about to relate were discovered.

But before I proceed, I might add that while some of these sea-squirts
lead solitary lives, fast anchored to the rock or sea-weed, others form
colonies, while yet others, and more distantly related forms, are
transparent and swim, sometimes in countless millions, at the surface of
the sea, covering an area of several miles. Some of the stationary forms
make coats for themselves of sand, others build them houses to live in.
While most are dull-coloured, some are, on the contrary, very
brilliant. Their range in size is no less varied, some being almost
microscopic, while others attain a length of as much as four feet.

But though so different in their adult stages, they all begin life as
vertebrated or backboned animals, though in some this stage is more
perfect than in others.

[Illustration: FIG 2 FROG--TADPOLE]

[Illustration: FIG 1 SEA SQUIRT--TADPOLE]

As you will see in the illustration (figs. 1 and 2) of one of these
youngsters, the resemblance to the tadpole of the frog is most striking,
and in some of the points wherein the sea-squirt differs from the
tadpole, it represents a yet earlier structural stage which frogs have
long since passed through, and no longer repeat in the course of their
growth. Take the case of the eye, for example; this in the young
sea-squirt lies embedded in the brain, and is only dimly able to
perceive light received through the transparent head; but the eye of all
the backboned animals is really an outgrowth of the brain which has
forced its way to the surface; here we see it in its primitive or
original condition. The mouth in the young sea-squirt, again, opens on
the top of th