The Porcupine-fish, as his name tells us, is one of these.  He is a small fish, living in warm seas.  No doubt he has many enemies, eager to meet him and eat him.  But, when they see this little fish puff out his sides like a balloon, and when pointed spines rise up all over the balloon, they think better of it!  They leave him alone; and the Porcupine-fish goes back to his usual shape, the spines lying flat until wanted again.  He is sometimes called the Sea-hedgehog or Urchin-fish, and well deserves his name.

Many of the Skates or Rays wear terrible spikes.  The Starry Ray (p. 52, No. 7) is not easy to handle, dead or alive, for he has spines all over his body.  The Thornback is another ugly fellow of this family, having spines on his back and a double row of them down his tail.  Fishermen are careful to avoid the lash of this armed tail.  The Sting Ray shows us still another weapon.  At the end of its long tail it has a horrible, jagged three-inch spike.  As this fish likes to bury itself in wet sand, bathers sometimes tread on it.  In a flash the tail whips round!  A poisonous slime covers the spike, causing great pain to the unlucky bather.

Several poisonous fish are common near our coast.  You may have seen the one called the Great Weaver, also its small cousin, the Sting Fish.  The Weaver is dreaded by fishermen; for the spines on its back fin, as well as the one on its gill-cover, cause poisoned wounds.  They are grooved, to hold a very poisonous slime.

Some fish have the power to kill their prey, and stun their enemies, at a distance!  Instead of a spiny defence, they are armed with electricity! The best-known sea-fish of this sort is the Electric Ray, also called the Cramp Fish or Torpedo (see p. 48).  It is a clumsy fish about a yard long, and very ugly.  Being too slow to catch its swift prey in fair chase, it stuns them with an electric shock, and then eats them.  The electric power comes from the body of the Ray; if it wishes it can send a deadly shock through any fish which ventures near.  Without chance of escape, it is at once stunned, and falls helpless.

We come now to some formidable dangers of the deep—­big strong fish, so well armed that they roam the seas without fear.  On page 52 you see a picture (No. 2) of the Saw-fish, one of the Shark family.  It is a large fish, and carries a big saw on its head, with which it stabs sideways at its prey.

Imagine, if you can, a Shark about fifteen feet long and weighing a ton or so.  Now suppose the top jaw of this monster to be drawn out into a hard, flat blade six feet in length.  Then suppose there are sharp ivory teeth, one inch apart, fixed on each side the blade, and you have an idea of the Saw-fish.  This strange Shark is said to be as strong as it is fierce.  It kills its prey by tearing them open with side blows from its sharp, two-edged saw.  Its big mouth is fitted with a great many rows of needle-like teeth.