THE WORM AND LEECH TRIBE. 313 
PB bodies. The shell is exuded from 
Wy. "4, the body of the animal just as the 
yy, covering of a Crustacean is. In 
Wer the figure one of the animals is 
ZS ‘stretched up out of its shell, spread- 
= ing forth its delicate gill-tufts 
which are arranged around its 
head. It can withdraw itself’ en- 
iG tirely within the tube, and when 
it does so there is a provision for 
shutting it up. You see that one 
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“4 ELAN 7X 
al \ " of the long filaments is expanded 
eel \ UU) at the end into a flat, circular disk. 
Ne, This is the door which shuts down 
aed on the mouth of the tube after the 
Hig, 248-—Group of Serpule- ther filaments are all drawn in. 
537. There are other animals of this group which, in- 
stead of having a tubular shell exude from their bodies, 
form one by connecting together, with a gummy sub- 
stance from the mouth, particles of shell, sand, small peb- 
bles, ete. They are in this respect like the larve of the 
The Terebella, Fig. 247, does this. 
It is here represented 
with its tentacula ex- 
tending out from the 
tube. These are used 
in gathering its food. 
If you take a Terebella, and, breaking up its tube care- 
fully, get the animal in its naked state, you can, by 
placing it in some moist sand, see the process by which 
it forms a new tube. In doing this it takes each grain 
into its mouth, and then, turning its head backward, 
places it in its proper position. 
538. The third order is that of the Terricola, so called 
because they live in the earth. The Earthworm works 
through the ground by insinuating its pointed head be- 
tween the grains of dirt, pushing itself forward by some 
O 
