THE MAILED WARRIORS OF THE SEA. 157 
antennae, are really a part of the mouth. Lastly we 
have the prawn with his head and shoulders joined 
into one like the spider (in the lobster you may see 
a curved line marking the spot where these are 
joined), with five pair of legs, while some of its rela- 
tions have many more ; and the usual ringed abdo- 
men which in this case has little paddles under it 
for swimming. 
Now just as when we feed, part of our food goes 
to make phosphates, which form and strengthen our 
bones or internal skeleton, so do all these animals 
make out of the food in their bodies a substance 
called cJiitine something like horn, and this is 
deposited in the outer layer of their skin, and 
makes a firm skeleton all over the body, and eyes, 
and antennas, and legs ; and within this firm skele- 
ton the soft animal lives, much as a soldier in olden 
times was enclosed in his jointed armour. But if a 
soldier had been placed in armour as a baby, he 
would have had to change his suit many times before 
he became a man, and this is also the case with 
insects. Their covering is not like that of the sea- 
urchin, which we saw could be added to at every 
point ; it is made once for all, like the soldier's 
armour, and the creature must throw it off when it 
becomes too small for its body. Thus the prawn, the 
centipede, the spider, and the caterpillar alike creep 
out of their armour many times in their lives, leaving 
it often standing so perfect that it looks like the 
creature itself. 
We see then that the prawn and his relations, 
although they live in the sea, belong to the ringed 
and jointed-footed division, and are formed on the 
