144 
LIFE AND HER CHILDREN. 
Fig. 52- 
other making a diamond -shaped lattice -work like a 
netted purse, in the third they run along the body 
from head to foot. When the 
leech wishes to lengthen his body 
he contracts the round rings and 
so forces the long cords to stretch, 
making himself long and thin ; 
when he wishes to shorten his 
body he contracts the long cords 
and forces out the rings, making 
himself short and stout, while the 
criss-cross muscles help to modify 
these movements. 
So much for the muscles, and 
now for the telegraph which go- 
verns them. If you were to lay a 
dead leech on its back and open it, 
you would see running from end 
to end of its body a white cord (c) 
with little swellings of white mat- 
ter (g) at intervals upon it, and 
from these swellings very fine 
white threads (;/) are seen branch- 
ing out into the body. The cord 
is made of nerve-threads clinging 
closely together, and is so to 
speak the line of telegraph ; the 
swellings are masses of nervous 
matter called ganglia, and are the 
telegraphic stations ; the white 
threads are simple nerves carrying messages to the 
muscles ; while round the neck of the leech is a collar 
* Hirudo medicinalis. 
After Moquin-Tandon. 
Section of a Leech,* to 
show the nerve-cord c, 
with the ganglia or knots 
of nerve-matter g, and 
the nerves n, branching 
off from them ; s, walls 
of segments of the body ; 
p, pockets of slime. 
