e head instead of in the front, which is here modified to
form a sucker. But the gills, by which this little creature breathes,
expel the water by which they are bathed through a single hole at the
side of the head, as in the frog tadpole; while in the possession of a
brain, a spinal cord, and a soft backbone, both sea-squirt and tadpole
agree.

[Illustration: FIG 3 A YOUNG SEA SQUIRT CUT IN HALF AFTER THE
TRANSFORMATION HAS GOT WELL ADVANCED]

Thus, then, the captor of one of these baby sea-squirts though he knew
nothing of the peculiar after-history of the creature, would yet be sure
that he had here a very young or 'larval' stage of one of the backboned
animals. But he would be surprised indeed, as he watched the career of
this little creature, to find it grow daily more sluggish, and at last
fix itself by the sucker at the front of its head, and there remain as
if in 'the sulks.' From this time onwards the change for the worse
grows rapidly. This creature, as if indifferent to the great
possibilities before it, or caring nothing for the good name of its
race, speedily degenerates. As it will use none of the good gifts of
Nature, one by one she takes them away--eye and brain are the first to
go; then the tail begins to grow less and less (you can see the last
remnants of a tail in fig. 3), and finally there is neither head nor
tail, power of sight, nor power of motion; all that remains is an
irregular-looking leathery lump, which scarcely seems to be alive (fig.
4). It feeds by drawing water through a hole at its upper end into a
great throat pierced by gill-slits (shown in fig. 5, which represents a
sea-squirt with the outside wall cut away); the water passes out through
the slits into a big chamber. From this chamber the water escapes by
another hole (marked 'discharge' in fig. 5) to the outer world again;
meanwhile, the food, consisting of microscopic animals, has been caught
by a moving rope of slime running along the back of the throat, and so
into the stomach. But what a fall! Think of it--a career full of
promise, the equal of that of vertebrate animals, ending in an
ignominious surrender of its birthright, and a drop to the level of the
humble oyster!

[Illustration: FIG 4 LIVING SEA SQUIRT]

[Illustration: FIG 5 SQUIRT SECTION OF A SEA SQUIRT. THE OUTSIDE WALL OF
THE BODY HAS BEEN CUT AWAY TO SHOW THE GILL OPENINGS, THROUGH ONE OF
WHICH AN ARROW ESCAPES, WHILE ANOTHER ENTERS THE MOUTH]

W. P. PYCRAFT,