All urchins

are supplied with eggs, but in some of the species the
eggs are exceedingly small and unfit for food. Singularly enough,
the urchin has what we may call its head and mouth down below, and a
place for the issue of the residuum up above; (and this same
property is common to all stromboids and to limpets). For the food
on which the creature lives lies down below; consequently the mouth
has a position well adapted for getting at the food, and the excretion
is above, near to the back of the shell. The urchin has, also, five
hollow teeth inside, and in the middle of these teeth a fleshy
substance serving the office of a tongue. Next to this comes the
oesophagus, and then the stomach, divided into five parts, and
filled with excretion, all the five parts uniting at the anal vent,
where the shell is perforated for an outlet. Underneath the stomach,
in another membrane, are the so-called eggs, identical in number in
all cases, and that number is always an odd number, to wit five. Up
above, the black formations are attached to the starting-point of
the teeth, and they are bitter to the taste, and unfit for food. A
similar or at least an analogous formation is found in many animals;
as, for instance, in the tortoise, the toad, the frog, the stromboids,
and, generally, in the molluscs; but the formation varies here and
there in colour, and in all cases is altogether uneatable, or more
or less unpalatable. In reality the mouth-apparatus of the urchin is
continuous from one end to the other, but to outward appearance it
is not so, but looks like a horn lantern with the panes of horn left
out. The urchin uses its spines as feet; for it rests its weight on
these, and then moving shifts from place to place.