96 LIFE AND PIER CHILDREN. 
We see, then, that the tiny urchin which came out 
of the jelly-animal No. 4 grew up strictly according 
to the true ray-like (cr radiate] plan, and yet what a 
change he has made and what a snug home he has 
formed round his body ! 
By laying down plates of lime within his soft flesh 
he has built a strong box, in which all his soft parts 
are enclosed, and at the same time has managed to keep 
a complete communication with the outer world. His 
sucker-feet, which act exactly like those of the star- 
fish, lie safely within the box till he needs them, and 
then each one is put out at a tiny hole like a pin- 
prick in one of the rows (///). The porous plate 
(wJi) supplying them with water is at the top of the 
shell in the back, where it would be in the star-fish, 
and in the other plates near it are the openings out 
of which it passes its eggs. But where are its eyes ? 
Consider for a moment where they ought to be upon 
the star -fish plan. At the tip of each ray, and 
therefore, when the rays are turned up so that the 
tips meet round the back, they will be at the top of 
the shell, where you will find five small holes contain- 
ing eyes (e), not so perfect as those of the star-fish 
but sufficient to see light. 
Could a stronger or safer fortress have been 
designed even by the most ingenious engineer? No 
single soft spot is left bare to attack except the skin 
round the mouth, and this is always turned to the 
ground and defended by the spines projecting on all 
sides. The mouth itself is a most complicated piece 
of mechanism, with five strong teeth set in powerful 
jaws, which lie inside the shell. 
And now how is this box to grow ? The tiny 
