ELASTIC-RINGED ANIMALS. 145 
of nerves with two large ganglia, the head telegraph 
offices. Now, it is this system of nerves which enables 
the leech to give orders to its muscles so rapidly, 
and throughout all the ringed animals this same 
system is found growing more and more perfect up 
to the ants. 
When the leech- is alive and uninjured, all the 
telegraphic stations work together, and you will notice 
that in the middle of the body, which is divided into 
segments (s), each has its own station or ganglion, 
and though all these usually work together, yet each 
segment is so active that if the cord is cut in half in 
the middle, the stations in the tail end of the leech 
will work on their own account and the two halves 
will often try to pull different ways. We see then 
that we have here a very powerful machine, and when 
we remember that the leech has eight or ten simple 
eyes set in its back near the head, and two strong 
suckers to cling with, within one of which is a mouth 
armed with three saw-like jaws which can easily pierce 
the skin of its victim, already made tight by the 
sucker, we can understand that he is well fitted for the 
battle of life. He is essentially an aquatic-breathing 
animal ; and though he can live for some time out 
of the water, he can only do so in very damp air, 
and his body is always covered with slime which 
oozes out from some little round pockets (j>) in the 
sides of his body. 
So the leeches live in ponds, and ditches, and 
marshes, and some even on damp land ; and the eggs 
out of which the young leeches come, are laid in co- 
coons of gummy slime placed in the holes and clay of 
the banks. Fish, snails, limpets, and grubs are their 
