THE MAILED WARRIORS OF THE SEA. 165 
hairs or cilia swept the water over the gills (see p. 1 09) ; 
but here, by a most beautiful arrangement, too com- 
plicated to explain, the movement of the feet near 
the mouth empties the water out, and so draws in 
fresh constantly from the back. And here again 
notice that animals without back-bones do not breathe 
through their mouths, but through their sides. 
Meanwhile our prawn has been swimming and 
feeding, and you will scarcely wonder at his activity 
or his quick senses, when you learn that the same 
double chain of nerves which we saw in the leech 
runs also under his body (g, Fig. 58), only that 
whenever two rings are quite lost in each other, two 
nerve masses or telegraph stations are also joined 
into one, so that in the head, for example, a large 
number have come together, and make powerful 
head-stations (Jig, Fig. 58) of nervous power. His 
muscles too are firm and strong, and fill nearly the 
whole of his ringed abdomen, and of his legs and 
claws, so that though he looks so transparent and 
fairy-like, he is stronger than he appears. 
But now there comes a time when he grows 
restless and uneasy, and ceases to care for food as he 
wanders about the rocks on the tips of his toes, seem- 
ing rather to be seeking some particular spot. The 
fact is that it is nearly a fortnight since he has changed 
his armour, and as he is young and growing fast, it 
begins to be very tight for him. At last he finds 
a spot to his liking, and taking hold firmly by his 
feet, he begins to sway to and fro so as to loosen his 
body inside its covering. Then all at once a slit 
opens between his shield and the skin of his abdomen, 
and gradually his shoulders and head back out, bring- 
