all--the body that is to be begins to be formed. To
grasp this thoroughly, first of all take such a rubber ball as I have
described, and push in one side. Compare it with the illustration (fig.
2).

[Illustration: Fig. 3.--Young Starfish, third stage.]

Soon after the formation of the mouth, our growing starfish develops his
first organs of locomotion. Now, these are neither arms nor legs, but
take the form of short hair-like growths, endowed with the power of
rapid waving motion, whereby the body is propelled through the water.
These are to be seen in the picture of one of these little creatures,
shown for clearness sake as if cut in half. (Fig. 3.)

[Illustration: Fig. 4.--Nearly full-grown Starfish.]

A little later our young starfish has assumed a new shape. Here there is
a large mouth and stomach, while the swimming hairs have all been cast
off except a few arranged in the form of two bands; and, later still,
the creature takes the extraordinary form shown in fig. 4. Swimming by
the motion of waving hairs is now a thing of the past; instead, long
arms have been developed, which perform this work much more effectually,
and these arms are supported by a hard, chalky skeleton. Soon another
little pushing in of the body takes place, and, lo, out of this grows
the body of the starfish that is to be! (as is the middle of fig. 4). In
about forty-five days from the beginning of this eventful history, the
feet and body appear sticking out of the body, whose growth we have been
watching; and, in a very short time after, this chalky skeleton is
destroyed, and the rest of this infantile body cast away, leaving the
fully formed starfish with an entirely new skeleton! Thus, then, wonder
of wonders, this curious creature possesses during its lifetime _two
distinct skeletons_!

[Illustration: Fig. 5.--Young Sea-urchin.]

[Illustration: Fig. 6.-Young Rosy Feather-star.]

The sea-urchin and sea-cucumber undergo similar changes. (See fig. 5.)
So also does the beautiful rosy feather-star, but with certain
modifications too interesting to be passed over. In what we call its
larval body, or its period of childhood, the body takes the form of a
cylinder, as you see in the picture, with a little tuft of swimming
hairs at the bottom, and bands of the same round the body (fig. 6.)
Within this body, as in the starfish, a new body is gradually formed.
Then, as you see in the picture, the inside of the egg-shaped body takes
the form of