THE OUTCASTS OF ANIMAL LIFE. 141 
the muscles of the pig. All these, and hundreds 
of forms like them, belong to that wandering band 
of outcasts, which have been driven from the face of 
the earth to feed upon the strength of others. They 
are not a pleasant band, but they teach us most 
surely the truth that the children of Life are sown 
broadcast over the earth, to make the utmost use of 
it that can be made. We have even examples where 
a parasite upon some animal has another parasite 
within it ; as when by cutting open a snail, worms 
are found within, and these worms when cut open 
are found to be the home of some tiny infusorian or 
slime animal, so that even within the body of one 
animal we have a little world of life. 
Another truth it teaches us which we have noticed 
before ; namely, that where a creature has little use for 
its powers, these diminish and it becomes degraded 
and feeble ; for the parasitic worms, with their low 
structure, their want of eyes and ears, and often of 
mouths and stomachs, are most of them poor miser- 
able creatures at best. Yet still we find even here 
that each must do some work. The most shiftless 
of worms passed on passively from one animal to 
another, must find its way to the liver, or the muscle, 
or the intestine which is its natural home ; and in 
the hooks and suckers, and daggers so admirably 
fitted for opening a path, and clinging firmly when 
the right spot is found, we see a proof that even 
these poor debased parasites have acquired some 
weapons in the struggle for life. 
But we must not stop here in our history of the 
worm tribe, for these parasites have distant relations 
