y with food and shelter and everything else it wants. So far as
the result to itself is concerned this arrangement may seem at first
sight satisfactory enough; but when we inquire into the life history of
this small creature we unearth a career of degeneracy all but
unparalleled in nature.

The most certain clue to what nature meant any animal to become is to be
learned from its embryology. Let us, therefore, examine for a moment the
earliest positive stage in the development of the Sacculina. When the
embryo first makes its appearance it bears not the remotest resemblance
to the adult animal. A different name even is given to it by the
biologist, who knows it at this period as a Nauplius. This minute
organism has an oval body, supplied with six well-jointed feet by means
of which it paddles briskly through the water. For a time it leads an
active and independent life, industriously securing its own food and
escaping enemies by its own gallantry. But soon a change takes place.
The hereditary taint of parasitism is in its blood, and it proceeds to
adapt itself to the pauper habits of its race. The tiny body first
doubles in upon itself, and from the two front limbs elongated filaments
protrude. Its four hind limbs entirely disappear, and twelve
short-forked swimming organs temporarily take their place. Thus
strangely metamorphosed the Sacculina sets out in search of a suitable
host, and in an evil hour, by that fate which is always ready to
accommodate the transgressor, is thrown into the company of the
Hermit-crab. With its two filamentary processes--which afterward develop
into the root-like organs--it penetrates the body; the sac-like form is
gradually assumed; the whole of the swimming feet drop off--they will
never be needed again--and the animal settles down for the rest of its
life as a parasite.

One reason which makes a zoologist certain that the Sacculina is a
degenerate type is, that in almost all other instances of animals which
begin life in the Nauplius-form--and there are several--the Nauplius
develops through higher and higher stages, and arrives finally at the
high perfection displayed by the shrimp, lobster, crab, and other
crustaceans. But instead of rising to its opportunities, the sacculine
Nauplius having reached a certain point turned back. It shrunk from the
struggle for life, and beginning probably by seeking shelter from its
host went on to demand its food; and so falling from bad to worse,
be